A controlled vent and burn of toxic chemicals at the train derailment in East Palestine, Ohio, went "as planned," and "no concerning" air and water quality readings have been detected, Pennsylvania Gov. Josh Shapiro said Monday night.
"For now, out of an abundance of caution, Pennsylvanians who live within two miles of East Palestine, where this derailment occurred, should just continue to shelter in place this evening and keep your windows and your doors closed," Shapiro said.
Crews monitoring air quality “have not seen anything” unexpected, the Environmental Protection Agency said during an evening press conference with local officials.
“So far, so good. And we’re going to continue to monitor until the fire’s out,” James Justice of the EPA said.
A large ball of fire and plume of black smoke could be seen earlier Monday as the burn took place.
The news comes after officials made urgent calls for evacuations as they planned to burn off the chemicals from the Norfolk Southern train in order to avoid a major explosion.
A 1-mile mandatory evacuation zone remained in place around the derailment Monday night, with no timeframe for when residents will be allowed back in, according to East Palestine Mayor Trent Conaway.
In an earlier statement to ABC News, Norfolk Southern called the controlled release a success and said materials were burning off according to plan.
The railroad also said it is monitoring air quality with the Ohio EPA.
Residents in a 1-mile by 2-mile area surrounding East Palestine -- which includes parts of Ohio and Pennsylvania -- must evacuate immediately, Ohio Gov. Mike DeWine had said.
"The vinyl chloride contents of five rail cars are currently unstable and could potentially explode, causing deadly disbursement of shrapnel and toxic fumes," the governor's office said in a statement. "To alleviate the risk of uncontrollable shrapnel from an explosion, Norfolk Southern Railroad is planning a controlled release of the vinyl chloride at approximately 3:30 p.m. today."
Officials released a map showing a red zone and a yellow zone, downwind from the burn, with Norfolk Southern saying anyone who remains in the red area will be exposed to deadly toxins and anyone in the yellow area could suffer "skin burns and serious lung damage."
The train, traveling from Illinois to Pennsylvania, derailed around 9 p.m. Friday, ignited and prompted a response from more than 50 fire departments across three states, according to Conaway.
Janet Meek, who lives about one block from the railroad tracks, said she heard a "loud boom" around 9 p.m. Friday. Her husband reported seeing a "billowing ball of fire" while walking their dogs.
The National Transportation Safety Board said Sunday that two videos show preliminary indications of mechanical issues on one of the rail car's axle. The train's emergency brake was activated after crews said an alarm went off, according to the NTSB. There were no injuries, the agency said.
Fire chief Keith Drabick told reporters Saturday that the train was carrying hazardous substances but could not confirm if the fire impacted the train cars carrying the hazardous goods. Drabick said the odor permeating East Palestine was not harmful at current levels, but representatives from the Environmental Protection Agency were monitoring the situation.
East Palestine is a small village on the border of Pennsylvania and Ohio with roughly 4,700 residents.
Efforts to contain the fire stalled Saturday night when firefighters withdrew from the blaze due to concerns about air quality and explosions.
Conaway said firefighters withdrew from the fire Friday night due to concerns about air quality, with a plan to reengage once they get a "better grasp of what exactly is what chemical is burning." At Saturday's press conference, Drabick said there had been multiple explosions overnight, which posed a risk to firefighters.
ABC News' Darren Reynolds, Matt Foster, Teddy Grant and Melissa Gaffney contributed to this report.