A blast at a power plant in Middletown, Connetticut killed five people and left more than a dozen injured on Sunday.

The explosion occurred at 11:25 a.m. as workers purged a natural gas pipeline inside the Kleen Energy Systems power plant, Middletown Mayor Sebastian Giuliano said, according to CNN. The blast was felt at residences 20 miles away from the plant, according to several witnesses who described it felt like an earthquake.

Search crews continued looking for victims who may be trapped under the rubble early Monday, WFSB reported. State and federal investigators were expected to launch an investigation today.

Kleen Energy Systems is an under construction natural gas power plant with a generation capacity of 620 megawatts. It was scheduled to go online in the fall and supply energy to 500,000 residents.