A steam pipe explosion in Manhattan’s Flatiron District sent massive plumes into the sky Thursday morning over New York City.

Update 3:05 p.m. EDT July 19: New York City Mayor Bill de Blasio said tests have confirmed that an 86-year-old steam pipe that exploded in Manhattan early Thursday was lined with asbestos.

The explosion, reported just before 6:40 a.m. near the intersection of 21st Street and Fifth Avenue, sent a massive smoke plume into the air and prompted authorities to evacuate dozens of buildings. New York City Fire Department Commissioner Dan Nigro said five people suffered minor injuries in the explosion.

De Blasio said streets closed by Thursday morning’s explosion would remain so until at least Saturday to give authorities the opportunity to clean the facades of the affected buildings.

“Our concern is the debris that was thrown off by the rupture,” he said. “Some of that is still visible on the street and on the building facades -- that all needs to be cleaned up.”

He said officials will conduct an assessment to ensure no asbestos remains in the area before they open it back up for business and residents.

Officials said the air cleared of asbestos shortly after the explosion, however, authorities warned people who were in the area during the incident that they should bag their clothing and shower.

“The challenge is anything that might cause repeat exposure,” de Blasio said. “One time brief exposure is generally not a problem.”

Update 12:50 p.m. EDT July 19: Streets closed Thursday morning when a nearly century-old steam pipe exploded in New York City could remain closed for several days if officials confirm the pipe was lined with asbestos, according to The New York Times.

New York City Fire Department Commissioner Dan Nigro said officials were working under that assumption on Thursday because the pipe was installed in 1932.

City officials told the Times that the exteriors of buildings in the area will have to be decontaminated if asbestos is confirmed.

In a statement obtained by WPIX, officials with the utility company Con Edison warned people to stay clear of the area of the explosion, on 5th Avenue and 21st Street in Manhattan.

“Environmental testing is being conducted to determine whether asbestos or other contaminants are present, but as a precaution anyone in the vicinity of the rupture who was covered in material is advised to bag their clothing and shower,” the statement said.

According to The Associated Press, there are more than 100 miles of steam pipes running beneath Manhattan. 

Update 11:15 a.m. EDT July 19: New York City Fire Department Commissioner Dan Nigro said five people suffered minor injuries when a high-pressure steam pipe that was installed in 1932 exploded Thursday morning.

“The major disruption is that not only did this steam line burst, but it caused the disruption of a gas line, a water main and some electrical power,” he said Thursday at a news conference.

Officials said 28 buildings were evacuated by 11 a.m. Thursday, up from the 11 reportedly evacuated in the immediate aftermath of the explosion.

Nigro said authorities sent samples to be tested for asbestos because of the age of the burst pipe.

“We are operating as if the samples will come back positive,” Nigro said.

Original report: According to WNBC, the blast occurred about 6:30 a.m. EDT Thursday near the intersection of 21st Street and Fifth Avenue.

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Authorities have not reported any injuries in the explosion, which "spewed debris all over the streets," the news station said.

Fire crews were still at the scene an hour later, and officials closed streets in the area as commuters headed to work.