NEW YORK (CNN) -- A steam pipe burst in midtown Manhattan Wednesday, causing a transformer to explode and sending thick plumes of steam and ash into the air near Grand Central Terminal, New York officials said.

Hundreds of people fled as dozens of police, fire and utility workers arrived. The blast left a huge crater, witnesses said.

New York Presbyterian hospital said it had received three people with injuries related to the explosion. Two of those patients were critically injured.

Video from the scene showed steam and mud spewing from underground and a small school bus with its windows and a door blown out.

Jim Margolin in the FBI's New York office said there is no indication there is anything "suspicious" about the explosion, though the FBI is still collecting information from city agencies and officials.

"A steam explosion on East 41 Street from Third and Lexington Avenue is not terrorist-related," said New York Police Department Deputy Commissioner Paul Browne in a statement.

Browne, speaking to CNN, said the explosion was "major."

"The ground was literally shaking under your feet," he said.

Andrew Troisi of the New York Office of Emergency Management said people in the area who do not need to be there should leave.

"This is a rescue operation. We have not begun to really detail the possible contaminants in the area, but there's a very good chance that hazardous materials are in the air," he said. "Let's not take any chances."

Police said they were reopening Grand Central Station, but subway lines near the explosion have been rerouted to bypass the Grand Central terminal stop, according to the Metropolitan Transit Authority.

The New York Fire Department said it received a call reporting an explosion at 5:56 p.m. More than 170 firefighters had been dispatched.

Former CNN reporter Adaora Udoji, now with CourtTV, said the scene at the time of the blast was "pandemonium."

"It felt like an earthquake. We saw hundreds and hundreds of people running down Third Avenue," she said. "They were screaming, they were crying."

The emergency response was "instantaneous," she said -- within about 20 minutes the entire area was locked down.

Udoji said the blast left a crater "many dozens of feet wide," comparing it to the craters she saw after bombings during a stint in Iraq. She also said a "hissing noise" can be heard for blocks.

Power company ConEdison provides steam power to about 1,800 commercial and residential customers in Manhattan from the Battery to 96th Street, according to the utility's Web site. Steam sales account for less than 10 percent of ConEdison's sales.

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