EAST PALESTINE, Ohio: Following a Monday warning to residents near the Ohio-Pennsylvania state line to leave immediately or risk death, crews released toxic chemicals into the air from five derailed tanker cars that were in danger of exploding and started burning it.

Late in the day, about an hour after officials announced the start of the controlled release, flames and black smoke erupted from the derailment site.

Authorities said they were closely monitoring the air quality despite a sizable plume of vinyl chloride being created above the village of East Palestine as a result of the slow release of the chemical from five rail cars into a trough and subsequent ignition.

“Thus far, no concerning readings have been detected,” Pennsylvania Gov. Josh Shapiro said at a brief evening news conference about three hours after the venting and burning procedure began.

He did, however, advise Pennsylvanians within a 2-mile (3.2-kilometer) radius of the derailment site to remain indoors and keep their doors and windows closed throughout the evening as a safety measure in case the wind shifted. Shapiro added that he had spoken with President Joe Biden, who had promised Pennsylvania and Ohio "the full support of the federal government."

Earlier this week, Ohio Governor Mike DeWine issued an evacuation order for the vicinity of the derailment, which has been smoldering since Friday night. Authorities were knocking on doors once more before releasing the vinyl chloride inside the cars, he said, even though they thought most, if not all, of the people in the danger zone had already left. "This is a life-or-death situation," DeWine said at a press conference. The controlled burn would release phosgene and hydrogen chloride into the air, officials warned.

Earlier, Norfolk Southern Railway's Scott Deutsch stated that carrying out this operation during the day would enable the fumes to dissipate more quickly and stop the rail cars from exploding and scattering shrapnel and other debris throughout the neighborhood.

We have no control over how that develops, he said.

According to him, the procedure entails using a small charge to puncture the cars, letting the material fall into a trench, and burning it off before it is released into the air. According to Deutsch, the teams in charge of the controlled release have accomplished this safely before.

A statement from Norfolk Southern Railway about three hours into the procedure stated that experts and first responders had breached the rail cars, chemicals were burning off, and the cars were anticipated to drain for a number of more hours.

The site is very close to the Pennsylvania state line, and a sparsely populated area of Pennsylvania is included in the evacuation zone. Before officials decided to use the controlled release on Monday, they had given about half of the 4,800 residents of East Palestine the weekend to leave.

According to Shapiro, the evacuation area includes about 20 houses in Pennsylvania. The last remaining residents needed help, and Pennsylvania State Police went door to door to make sure they left.

In a later statement, Shapiro claimed that he had been informed that residents within a mile (1.6 kilometers) of the controlled burn had vacated.

Authorities became concerned that the rail cars might erupt after a "drastic temperature change" was noticed in a rail car, forcing forced evacuations to start in East Palestine on Sunday night.

On Monday morning, locals were preparing their overnight bags, loading their pets into cars, and looking for hotel rooms. As the threat of an explosion grew, police in the village left their communication hub.

Streets leading to the area were blocked by police cars, snow plows, and military vehicles from the Ohio National Guard.

According to rail company Norfolk Southern and the National Transportation Safety Board, about 50 cars, including 10 that were carrying hazardous materials, derailed in a fiery collision on Friday night. There were no reported injuries to the crew, locals, or emergency personnel.

According to the National Cancer Institute of the federal government, five of them were transporting vinyl chloride, which is used to create the polyvinyl chloride hard plastic resin found in plastic products and is linked to an increased risk of liver cancer and other cancers.

According to federal investigators, a mechanical problem with a rail car axle was the reason for the derailment.

According to NTSB board member Michael Graham, the three-person train crew learned of the mechanical issue "shortly before the derailment." The exact "point of derailment" was located by investigators, but the board was still trying to identify which rail car had the axle problem, he said.

One person was detained for evading barricades up until the collision, according to village mayor Trent Conaway, who also declared a state of emergency in the area. He advised people to stay away or they would face arrest.

I don't understand why anyone would want to be up there; if you're that close, you're breathing toxic fumes, he said.