Five people have been injured after a steam pipe exploded beneath Fifth Avenue in Manhattan, hurling chunks of asphalt, sending a geyser of billowing white steam stories into the air and forcing pedestrians to take cover.

New York City Fire Commissioner Daniel Nigro said the five people suffered minor injuries and 28 buildings had been evacuated.

Three of the injured were civilians and the buildings will "remain evacuated for a while", he said.

Office of Emergency Management Commissioner Joseph Esposito says that if asbestos is found at the scene, the cleanup could take days.

Dozens of businesses have been effected, including having air conditioning and hot water shutdown in places.

The high-pressure steam leak was reported about 6.40 am local time.

The steam was still billowing about 10 stories high two hours later.

WABC reported there also were manhole explosions from West 19th Street to West 21st streets. Some subway trains were bypassing the area.

"I looked around and saw this big huge plume of steam shoot into the air," one witness, Daniel Lizio-Katzen, 42, who was riding his bike home to the West Village at the time, said.

"It was a pretty violent explosion," Lizio-Katzen told the Daily News.

"The steam was shooting up into the air about 70 feet. It was pushing up at such a high pressure that it was spewing all of this dirt and debris.

"The cars around were coated in mud ... It left a huge crater in the middle of the street."

Brendan Walsh, 22, a senior at New York University, had just gotten off a train and was headed to class when he saw the plume.

"The billows were about six stories high. There was a large scatter of debris," he said.

"I was standing behind the police line when a Con Ed worker came rushing over and screaming at police and firefighters to push everyone north because he was worried that there could be secondary manhole explosions.

"Everyone — including the police and firefighters who were standing by — started moving back."

Firefighters stripped off their heavy outerwear, bagged it and entered a red decontamination tent in their gym shorts and t-shirts to take showers.

Businesses were braced for the worst as the response dragged on and police and firefighters blocked access to buildings close to the explosion, crippling their neighbourhood and their workday.