At least two people were killed in Friday morning’s explosion at a northwest Houston manufacturing business, police said. The blast shook much of the city, damaged buildings up to a half-mile away and left some residents at least temporarily displaced.

The explosion rocked Watson Grinding and Manufacturing around 4:15 a.m. CT (5:15 a.m. ET), tearing apart several structures while sending debris and shock waves much further, pushing some nearby homes off their foundations, officials said.

“This is, in essence, a disaster area right now,” Houston Police Chief Art Acevedo said of the area roughly an 18-mile drive northwest of downtown.

An investigation into what caused the blast is underway and may take months, Acevedo said.

“We don’t have any evidence that an intentional act is involved,” but police and arson investigators and federal explosives experts will explore all angles, he said.

The debris field is so widespread — officials estimated between a quarter-mile to a mile away — police have asked residents for help with a potentially grim task: looking for human remains and other debris in their yards and on roofs.

“Look for any debris, any body parts, anything that may be related,” and call police if anything is found, Acevedo said.

Besides those killed, at least one person was injured by shattered glass and was taken to a hospital, Houston fire Capt. Oscar Garcia said.

The names of the dead haven’t been released, partly because investigators are waiting for small fires to burn themselves out before entering the blast site and confirming who was there, officials said.

But there’s a “high probability” they are two Hispanic men who worked for Watson Grinding and Manufacturing, Acevedo said. The two men’s vehicles are still at the plant and no one else from the company has been reported missing, he said.

Blast breaks windows and damages doors some distance away

A fireball rose from the scene after the blast, video posted to Twitter appears to show. The distant footage was taken by a camera mounted to a home window.

“I live downtown,” Houston fire Chief Samuel Pena said, “and I felt it all the way downtown.”

The business is in a strip of industrial and commercial businesses, surrounded to the west and east by homes. The nearest neighborhoods, Westbranch and Carverdale, were damaged most severely, Acevedo said.

Damage to homes included broken windows and doors, and in at least one case, a collapsed ceiling, CNN affiliates reported.

“The whole ceiling fell in,” a resident told KTRK about her home.

“I thought maybe the house had gotten hit by lightning. And then I realized there was no storm,” the resident told KTRK.

Mark Brady, who lives about a half-mile from the manufacturing business, told CNN affiliate KPRC the blast “knocked us all out of our 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.

Mayor Pro Tem Dave Martin said the city will work with various agencies to help move people into temporary housing.

“A lot of the houses in the neighborhood are not going to be livable for a number of weeks,” said Martin, temporarily standing in for Mayor Sylvester Turner, who was out of state.

It wasn’t clear how many homes and businesses were damaged. Pena said that out of roughly 190 homes assessed so far, most had some sort of damage.

Firefighters wait for small fires to burn out before exploring blast site

Some small fires still were burning hours after the blast, and firefighters will let those burn out by themselves before thoroughly searching the site, Pena said.

Earlier, propylene gas was leaking from a tank at the facility following the explosion, but crews eventually stopped it, he said.

The leaking gas dissipated, and a hazardous materials team has been monitoring air quality, Pena said.

“We have no concerns about the quality of the air we’ve been breathing,” Pena said.

Fire department inspectors are gathering information about the business’s full chemical inventory, and the company’s owner has been cooperating with the investigation, officials said.

Propylene is a colorless, flammable, pungent gas made from petroleum. It is most often employed to make polypropylene, a kind of plastic used in household products, from take-out meal containers to medicine bottles, and in automotive, industrial and textile products. Similar to propane, it burns hotter and can be used as fuel gas and to make acetone.

A temporary shelter has opened for people whose homes were damaged

A church in the area is serving as a temporary shelter “for anybody that we may have to evacuate out of their home due to damage,” Pena said.

Police at some point Friday cut off access to the damaged Westbranch and Carverdale neighborhoods, hoping to ward off potential looters.

But residents with identification will be allowed back into those areas Friday afternoon, Acevedo said.

“We want people to come back (partly) because we do want people to board up” their damaged homes, the police chief said.

At least two nearby schools closed for the day.

A school district in the area, Spring Branch ISD, said on Twitter that for schools in session, it “will keep all students inside today as air quality in the area continues to be monitored.”