A natural gas explosion destroyed a small apartment building Friday, critically injuring a man and forcing the evacuation of more than 40 people who live nearby, authorities said.

The blast destroyed the two-apartment building and damaged an adjacent building with three apartments and an office, Fire Chief Dana Miller said.

The injured man had unhooked a gas line in what was an apparent suicide attempt, Miller said. The man was flown to a burn center in Greeley, Colo., in critical condition.

Authorities cleared residents out of more than a dozen nearby apartments and turned off electricity and gas as a precaution.