Officials in Ohio and Pennsylvania said that crews have successfully released toxic chemicals from five tanker cars of a derailed freight train that were in danger of exploding.

The crews slowly released vinyl chloride from the tankers and moved into a trench, where it was ignited. Officials urged anybody living within a two-mile radius to shelter in place and keep their doors and windows closed because toxic chemicals, including phosgene and hydrogen chloride, would be released into the air.

Authorities said they were constantly monitoring the air quality around East Palestine during the burn.

"Thus far, no concerning readings have been detected," Pennsylvania Governor Josh Shapiro said during a press conference.

Officials said the plan is to wait for the flames to burn themselves out before crews move in and begin the process of removing the rail cars. East Palestine Mayor Trent Conaway said there is no timeframe for when residents will be allowed to return home.

"We have to wait til the fires die down," he said.

The National Transportation Safety Board said that the derailment was caused by a mechanical failure on one of the railcars' axles.

"The crew did receive an alarm from a wayside defect detector shortly before the derailment, indicating a mechanical issue," National Transportation Safety Board Member Michael Graham. "Then an emergency brake application initiated."

Investigators hope to learn more about what caused the crash once inspectors can access the site.

Traffic