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Mass transit in the Boston was suspended, colleges and universities classes canceled as the police sought the second suspect in the Boston Marathon bombings.

One Boston Marathon bombing suspect was killed Friday in a shootout with police and a manhunt was on in Watertown, Mass., for the second, officials said.

"Manhunt under way for Suspect #2 Dzhokhar Tsarnaev, 19, a Chechen resident of Cambridge," read a Twitter post by a Boston Globe reporter.

The suspects are brothers with the last name Tsarnaev, law enforcement officials told NBC News. The suspect still at large is 19 years old and has a Massachusetts driver's license, they said.

Authorities told NBC News the men had international ties and came to the United States about a year ago. Both had military experience, officials said.

Two bombs exploded near the finish line Monday, killing three people and injuring more than 170.

Massachusetts Bay Transportation Authority Police Capt. Paul MacMillan said the suspect was killed in a gunfight, CNN reported.

Police and the FBI were conducting a house-to-house in a 20-square-block area in Watertown for the second man, described as armed and dangerous and called "suspect No. 2."

WBZ-AM, Boston, reported a low-level "boom" where police detained at least two men near a cab in Watertown. They were taken away in an unmarked police car.

Watertown residents were told to stay indoors and businesses were told not to open their doors.

A police officer was killed at the Massachusetts Institute of Technology campus in Cambridge, Mass., Thursday before a vehicle was carjacked.

NBC News said the suspects battled law enforcement officers with gunshots and explosives. CNN said a loud bang was heard but no explosions had been confirmed.

Amtrak said its train service between Providence, Rhode Island, and Boston was suspended.

The MBTA shut down Boston-area bus, subway, commuter rail, and ferry routes.

Universities that announced they were closed because of the search include Harvard University, MIT, Boston University, Emerson College and Boston College.

Police in Watertown contacted residents by robocall, instructing them to stay in their homes, CNN reported.

NBC said the suspects approached an MIT police officer, shot him several times and stole his patrol car before robbing a 7-Eleven convenience store, hijacking a black Mercedes SUV and briefly kidnapping the driver.

"The victim was carjacked at gunpoint by two males and was kept in the car with the suspects for approximately a half hour. The victim was released at a gas station on Memorial Drive in Cambridge. He was not injured," the Middlesex District Attorney's office said in statement.

An MBTA officer was wounded in an exchange of gunfire between police and the suspects, and was listed in critical condition.

Unconfirmed reports indicated the dead suspect had an improvised explosive device strapped to his chest.