Originally Published: 10 APR 23 03:59 ET

Updated: 11 APR 23 10:32 ET

By Rebekah Riess, Amanda Jackson and Andi Babineau, CNN

(CNN) -- A shelter-in-place order has been lifted for neighborhoods near a burning fishing vessel in the Hylebos Waterway in Tacoma, Washington, officials said.

The vessel -- which was still burning Monday and believed to be carrying 55,000 gallons of diesel and 19,000 pounds of freon -- caught fire early Saturday morning while moored in the waterway, the US Coast Guard said in a news release.

The shelter-in-place order was issued after a "significant explosion" took place and fire conditions worsened, officials said.

By Monday, smoke conditions had improved. The US Environmental Protection Agency was still monitoring air quality, the Coast Guard said.

Crews were still trying to "cool the haul, as the fire burns itself out" with high-powered streams of water, the Tacoma Fire Department said Monday.

"While it appears that most of the flammable material onboard has burned, it is likely that smoke will continue to be visible throughout the day," the department said.

The explosion was linked to a heated compressed gas cylinder on the vessel, Port of Tacoma officials said Sunday night, citing fire officials.

"We were very fortunate that the fire was quickly spotted and reported and the crew onboard was able to safely evacuate," US Coast Guard Lt. Stephen Nolan told CNN affiliate KING-TV Sunday.

By Sunday, the fire had spread throughout the vessel and was about 100 feet from the ship's freon tanks, according to the Coast Guard. Freon is a trademark name typically used to refer to several different refrigerants, including chlorofluorocarbons, according to the EPA.

As the fire continues to burn, the heat from the flames can build pressure in the freon tanks, which have built-in heat-activated pressure relief valves designed to release pressure from the tanks in an emergency, according to the Coast Guard.

"While freon can be toxic if inhaled in large quantities or in a confined space, the release of freon into the atmosphere is not expected to pose any health and safety risks to the public," the Coast Guard said.

Still, the Tacoma Fire Department asked residents of the Northeast Tacoma, Browns Point and Dash Point neighborhoods to "remain indoors and limit exposures to smoke."

"Residents concerned about smoky conditions can provide additional protections by keeping doors closed and shutting outside air vents. Residents may also want to avoid any strenuous activity or exercise outdoors," the mayor tweeted.

The EPA has been monitoring the air in the surrounding areas, and first responders have deployed floating barriers around the vessel to contain any spills, according to the Coast Guard's news release.

The Coast Guard has also closed the Hylebos Waterway for all commercial and recreational vessel traffic.

As of Sunday night, no injuries had been reported and there were no signs of maritime pollution, the Coast Guard said.

As crews continue to battle the fire with cooling spray, it remains unclear what ignited the blaze. Authorities said the cause of the fire remains under investigation.