Workers were pushing coke out of huge ovens and preparing for maintenance when an explosion rocked a US Steel plant outside Pittsburgh, a company executive said Tuesday, a day after the blast killed two workers.

One person has died and dozens are reportedly injured or trapped under rubble following an explosion at a U.S. Steel plant near Pittsburgh on Monday, an Allegheny County emergency services spokesperson told the Associated Press.

The cause of the blast is still unknown. The Pennsylvania plant has racked up fines and faced lawsuits over emissions problems.