Originally Published: 30 AUG 21 13:48 ET

By WABC Staff

QUEENS, New York (WABC) -- New York Governor Kathy Hochul said Monday an "unprecedented system breakdown" led to half of the nation's largest subway system losing power Sunday night, stranding hundreds of riders and crippling service for hours.

Governor Hochul called the outage "unacceptable" and told the riders who found themselves stranded, "the system failed you." She's now calling for an internal investigation into the failure.

The series of events started at 8:25 p.m. when a Con Ed power surge forced the subway's signal system to switch to back up power. That secondary power supply held until about 9:10 p.m. when it mysteriously failed, an MTA spokesperson said, disabling signaling for all of the numbered trains as well as the L train.

Con Ed said a fault to an underground transmission feeder in Long Island City, Queens, is what caused the momentary voltage disturbance.

"The disturbance lasted a fraction of a second for all customers throughout our service territory," Con Ed said in a statement. "We remain in contact with the MTA to understand why they lost this communication at their rail center during the voltage disturbance."

An MTA spokesman said the outage did not affect the subway's third rail, which powers the individual cars. That means that people stuck on the trains still had lights and air conditioning, until some riders opted to self-evacuate into tunnels.

That added to the chaos, forcing the MTA to cut the power to four trains clustered around 149th St. Grand Concourse, leaving those riders in the dark without air conditioning.

Service was fully restored by 1:29 a.m on Monday.

At a press conference Monday morning outside MTA Headquarters in Lower Manhattan, Governor Hochul said more than 500 people either had to be evacuated or chose to self-evacuate, opting to leave trains on their own, navigating dark tunnels. With the third rail still active, she called that "dangerous" and urged people not to do that if it happened in the future.

Video from inside the 149th St. Grand Concourse station showed FDNY firefighters lifting people up off the tracks and onto the station platform. Riders told Eyewitness News they had little communication from the MTA.

"They kept saying they don't know what's going on. But an hour and 36 minutes we were trapped on the train. A long time. Kids, children, no water, nothing," one woman said.

Now, the MTA will conduct an "after-action" report to determine why the system failed. It is bringing in outside experts to conduct a full investigation.