Photo: The Canadian Press

Two people died after a massive explosion Friday levelled a warehouse in Houston, damaging nearby buildings and homes and rousing frightened people from their sleep miles away, authorities said.

The explosion happened about 4:30 a.m. inside a building at Watson Grinding and Manufacturing, which makes valves and provides thermal-spray coatings for equipment in various industries, authorities said. The building was reduced to burning rubble and debris, and some of the surrounding buildings suffered heavy damage to parts of their walls and roofs.

Police Chief Art Acevedo confirmed the deaths Friday. He said authorities don't believe the explosion was intentional though a criminal investigation is underway.

Acevedo asked residents who live nearby to search their homes and neighbourhoods for any debris — including body parts — and to contact police if they find anything that could aid in the investigation.

Houston Fire Chief Samuel Pena said hazardous materials crews have secured the valve on a 2,000-gallon (7,571-litre) tank of propylene that had been leaking. Propylene is a colorless gas used to produce chemicals in plastics, synthetic rubber and gasoline. It is highly flammable and can explode in a fire. People exposed to propylene can become dizzy and light-headed, and the gas can also cause liver damage.

Nearby homes sustained significant damage. Some were knocked off their foundations.

Danny Wilson, 63, who lives less than a mile from the site, said he was sleeping when his wife woke him up.

“She heard a big noise and the (grandkids) were running out of their rooms,” Wilson said. “She said it was some kind of explosion or somebody was trying to get in.”

Wilson said he first checked inside his home to make sure nobody had broken in and then he went outside and talked to neighbours to find out what was going on and to check for any damage.

“I didn’t notice any broken glass and I looked at the back window and it was shattered big time,” Wilson said.

He said the blast also broke glass on part of his front windows.

“Everybody seems to be OK now. That’s the main thing,” Wilson said.

Mark Brady, who lives near the site, told TV station KPRC that the explosion “knocked us all out of bed.”

"It busted out every window in our house. It busted everybody’s garage door in around here … and closer toward the explosion over here, it busted people’s roofs in and walls in," he said.

The blast shook other buildings, with reports on Twitter of a boom felt across the city. Pena said there were no reports of hazardous air quality, based on monitoring done by a hazardous materials team.