Originally Published: 02 SEP 21 04:08 ET

Updated: 02 SEP 21 12:18 ET

By Jason Hanna and Madeline Holcombe, CNN

(CNN) -- Water rescues still were underway Thursday across parts of the East after the remnants of Hurricane Ida unleashed deadly and paralyzing flooding at shocking speed across areas including New York City and Philadelphia.

The storm dumped rain at sometimes unprecedented rates Wednesday night -- several inches per hour -- bringing flooding that killed at least 15 people in New York, New Jersey and Maryland, with waters rushing into homes and vehicles.

Cars were left abandoned on Northeast streets after drivers fled roads that transformed into swift rivers, and southern New Jersey is cleaning up from a tornado that flattened homes.

In the Philadelphia area, the Schuylkill River was above major flood stage Thursday morning, swamping city streets, delaying the city's rail and bus services, closing city buildings and prompting Philadelphia leaders to urge people to work from home.

Rescuers were navigating boats through flooded streets Thursday morning in and around Philadelphia and northern Delaware, ferrying people from flooded homes.

In New York City, first responders rescued commuters from halted subway trains Wednesday night, while other travelers were stranded overnight in subway stations, some sleeping on benches with service suspended and no way to get to their destinations.

"New York is used to disasters, but you cannot imagine how much rain fell out of the heavens last night," New York Gov. Kathy Hochul told CNN Thursday morning.

"There's going to be a massive cleanup. I would urge people to stay home, check on your neighbors, make sure they're OK."

Beverly Pryce, a nurse from Queens, was among those who stayed overnight in a Manhattan subway station, having left her home Wednesday night to get to work, only for the flooding to bring everything to a standstill.

"(I've seen) nothing like this," she told CNN Thursday morning. "I didn't expect it to be this severe; I would not have left my house."

Emergencies were declared for New York state, New York City and New Jersey. In New York City alone, firefighters rescued hundreds of people from vehicles on flooded roads and hundreds more from the subway system, the city fire department said Thursday.

Nine of the deaths were reported in New York City -- most of them in Queens -- officials said. Five deaths were reported in New Jersey, and one in Maryland.

Most of those killed were found dead in their flooded homes. Three people -- a 2-year-old, a man and a woman -- were found dead in their flooded basement in Queens, the city fire department said.

In Passaic, New Jersey, a man in his 70s was found dead after floodwaters overtook the vehicle he was in, Mayor Hector Lora told CNN's Don Lemon.

In Elizabeth, New Jersey, four residents drowned in an apartment complex along the Elizabeth River, Mayor Chris Bollwage said.

In Maryland's Montgomery County, a 19-year-old was found dead Wednesday in a flooded apartment complex, and his death is preliminarily attributed to the storm, police said.

Northeast shocked by ferocity and speed flooding

The rate of rainfall was stunning and sometimes unprecedented.

New York's Central Park recorded its wettest hour on record, with 3.15 inches falling from 8:51 to 9:51 p.m. The park's total rainfall -- 7.13 inches -- was its fifth-highest total for one day.

Newark, New Jersey, received its highest one-day total on record: 8.41 inches.

The Northeast and Mid-Atlantic areas were under flash-flood watches earlier Wednesday as the remnants of Ida -- which made landfall in Louisiana on Sunday as a major hurricane and devastated parts of that state -- approached.

Ida transitioned from a tropical depression to a post-tropical cyclone over the Appalachians on Wednesday morning as it rolled into the Northeast. Heavy rain was expected -- but where, precisely, the heaviest rain would fall wasn't known until shortly before it happened, FEMA Administrator Deanne Criswell told CNN on Thursday.

"People are just shocked by this," Hochul, the New York governor, said. "I mean this is an event that we planned for -- we started deploying resources to the region the night before and in the morning before."

"But once that rain starts coming down and it's just unrelenting, there's nothing that the people can do other than look up with their jaws dropped and say, 'What is happening here?'" Hochul said.

After the storm, New York's subway system was temporarily halted with the exception of two lines due to the flooding, leaving many people stranded and unsure how they would get home.

Some were idled on a subway near Times Square around 1:20 a.m. after traveling from the US Open tennis tournament in Queens. Videos from the station showed a waterfall flowing off of the train car roof and onto people trying to get out -- as well as a drink kiosk being whirled around by the wind.

As water gushed into stations, first responders have been evacuating people from trains, Acting MTA Chair and CEO Janno Lieber said.

The city also instituted a travel ban for all non-emergency vehicles until 5:00 a.m.

Tornado touches down in South Jersey, while the north deals with flooding

Many towns in the North Jersey area reported massive flooding, damaging homes and businesses and forcing drivers to abandon their cars. In Clifton, a fire ambulance was seen submerged in the flood waters along with several other submerged vehicles.

In South Jersey, a tornado touched down in Mullica Hill, about 25 miles from Philadelphia. In two videos, debris can be seen twisting up in the tornado.

Homes were flattened in Mullica Hill -- though no deaths were reported there, Gov. Phil Murphy said.

"This is going to take some time to dig out of, there's no question about it," Murphy said Thursday, standing in front of one of the wrecked homes.

"I had just left the gym and headed in the same shopping area to a small sandwich shop. I parked my car and called my husband to see if he wanted me to bring home food," said Kristi Johnson, who recorded the videos and shared what she witnessed with CNN.

"While I was on the phone I looked out my driver's window and saw the swirling clouds and debris flying toward me. I rolled my window down and it sounded like a train coming. I hung up on my husband and started to drive away from it. It was extremely scary."

Meanwhile, Newark, the state's largest city, recorded its all-time wettest day Wednesday. And in Trenton, the state capital, officials advised residents in the Island neighborhood to evacuate by 8 a.m. Thursday.

Flooding in Philadelphia; 41 rescued from Pennsylvania school bus

Parts of Philadelphia area flooded, leaving some vehicles still underwater on city streets Thursday morning.

Several rescue teams were using boats to reach stranded residents in the area Thursday morning, including flooded apartments in Bridgeport north of Philadelphia, video from CNN affiliate WPVI showed.

About 50 residents had been rescued by 10 a.m. ET, and a few more blocks still needed to be checked, Bridgeport borough manager Keith Truman said. Similar rescuers were happening Thursday morning in the Roxborough neighborhood of Philadelphia, and near Wilmington, Delaware, other video showed.

Elsewhere in Pennsylvania, the storm had trapped a school bus in floodwaters Wednesday in Shaler Township. The school district and local volunteer fire company confirmed that 41 passengers were rescued from the bus.

Video shows a team of at least four wading through water nearly up to their waist to help the passengers onto a small boat. The rescued students were then transported safely to the high school, Shaler Area School District said.

With a flash flood emergency and tornado watch, Gov. Tom Wolf encouraged residents to stay home Wednesday and take the storm seriously.

"This is an extremely dangerous storm that is impacting the entire state," said Wolf according to a news release. "As we continue to monitor the conditions, I ask everyone to please stay home if you're able."

In Maryland, Ida's downpour flooded at least 12 apartments at the the Rock Creek Woods complex in Rockville, where a 19-year-old man was found dead. Rescue personnel evacuated dozens of people there, officials said Wednesday.

Three people and one firefighter were transported to hospitals for non-life-threatening injuries.

A tornado also touched down in the state, according to Bud Zapata, the Annapolis Fire Department Public Information Officer.

The tornado was reported to have touched down in a primarily commercial area of Annapolis. No injuries have been reported, but some private residences were damaged and there was an active gas leak in the area. Fire, police and other agencies are assessing damage, Zapata said.

The National Weather Service had tweeted that a radar-confirmed tornado was in the area and to "seek shelter if you are in the path of this storm!"