An oil rig exploded in Louisiana on Sunday night, injuring at least seven people, five of them critically, authorities said. Rescue crews on Monday continued searching for one worker who was missing.

The platform, located near St. Charles Parish in Lake Pontchartrain, ignited sometime around 7 p.m. local time. Residents nearby reported hearing a large explosion before the rig was engulfed in flames.

“My house actually shook,” Andrew Love told the Times-Picayune. “At first I thought it was a sonic boom or something, I had no idea what was happening.” Officials said Monday they knew of no serious structural damage outside the oil rig.

The City of Kenner Government said on Facebook that cleaning chemicals ignited on the surface of the oil rig, although it was unclear if the chemicals caught fire before or after the explosion. The rig was being cleaned at the time of the blast.

An oil rig is currently on fire in Lake Pontchartrain which caused the sound earlier tonight. We will keep you informed if this impacts SCP. — St. Charles Parish (@stcharlesgov) October 16, 2017

“Several people have been rescued from the active fire on the rig,” Antwan Harris, a spokesman for Jefferson Parish, said in a statement obtained by The Associated Press.

All of those injured were taken to nearby hospitals. Three remained hospitalized on Monday in critical condition. Four people were treated and released. Searchers continued looking for one person.

The platform is owned by Clovelly Oil Co. The rig was burning off residual oil on Monday, officials said.

During a press conference on Sunday night, officials said oil may be leaking into the lake. The Times-Picayune said water quality evaluations will be conducted to determine if the lake has been contaminated, but noted that Jefferson Parish’s drinking water comes from the Mississippi River and will not be affected.