A man who suffered extensive burns in a natural gas explosion on Monday night at a duplex in East Oakland is in critical but stable condition at Saint Francis Memorial Hospital in San Francisco, a hospital spokeswoman said.

The man, Leon Spencer, was being treated for burns covering 80 percent of his body. Spencer was taken to Highland Hospital in Oakland and then transferred to the burn unit at St. Francis overnight, hospital spokeswoman Linda Gillespie said.

Spencer’s home, located in the 2300 block of 87th Avenue, was rocked by the explosion just after 8 p.m. Monday, Oakland fire Battalion Chief Melinda Drayton said.

The cause of the explosion remains under investigation, according to officials with the fire department and PG&E.

A spokeswoman for PG&E said the company’s gas inspectors don’t believe the explosion was caused by a leak in their equipment.

“There have been no leaks or compromises identified,” spokeswoman Jana Morris said Tuesday morning.

Morris said PG&E tested its lines and equipment outside the home; equipment inside the home is the homeowner’s responsibility, she said.

The explosion caused the second story of the building to collapse onto the ground floor, where Spencer lived, and also shattered the windows of a neighboring property, Drayton said.

Firefighters initially responded to reports of a structure fire and arrived on scene at 8:04 p.m. to find Spencer in front of the home. He had been badly burned and was being treated by neighbors, Drayton said.

Four adults, including Spencer, and two children have been displaced due to the fire and are being assisted by the American Red Cross, spokeswoman Caitlin Cobb said.