Blasts near the finish line of the Boston Marathon killed two people and injured 22 others Monday, Boston police said.

The marathon itself, on its Facebook page, referred to the blasts as bombs. Authorities did not say immediately what caused the explosions.

Massachusetts General Hospital said it was treating 19 injured people; Tufts Medical Center reported that some injured were to be treated there as well.

The explosions sent smoke billowing into the air at Copley Square, turning a site of celebration into a mess of destruction.

Crowds had gathered in the area to watch the runners.

Out of an abundance of caution, the Lenox Hotel was evacuated, the Boston Globe reported, as authorities looked into possible security concerns.

Officials in other cities, including New York, tightened security as as result.

Mike Baingon, who works at the Atlantic Fish Company in Boston, said an explosion took place in front of the restaurant and that he was right by the front door at the time.

The explosions occurred at about 2:45 p.m., more than two hours after the first of the race’s nearly 27,000 runners had crossed the finish line, CNN Producer Matt Frucci reported.
The race was halted as was subway service into the area.

Troops from the Massachusetts National Guard were assisting police as well.

[Update, 5:51 p.m. ET] President Barack Obama is expected to deliver a statement at about 6:10 p.m. ET from the White House.

[Update, 5:35 p.m. ET] Google has established a person-finder related to the Boston bombings. People who are looking for someone or have information about someone can make reports there.

[Update, 5:31 p.m. ET] Boston police now appear to be backing away from their commissioner’s earlier statement that a third incident  at the JFK Library 5 miles from the finish line – might have been related to the Boston Marathon blasts.

[Update, 4:30 p.m. ET] Boston firefighters have found what they believe is an unexploded device after the blasts, a government official said, according to CNN’s Joe Johns.

[Update, 4:02 p.m.]  A Massachusetts General Hospital spokeswoman tells CNN 19 victims  have been brought in.

[Update,3:57 p.m. ET] On their Twitter page, Boston marathon officials made this announcement: “There were two bombs that exploded near the finish line in today’s Boston Marathon. We are working with law enforcement to understand what exactly has happened.”

[Update, 3:53 p.m. ET] New York is taking precautions as a result of the explosions at the Boston Marathon.

In a written statement, New York Police Department Deputy Commissioner Paul Browne said: “We’re stepping up security at hotels and other prominent locations in the city through deployment of the NYPD’s critical response vehicles until more about the explosion is learned.

[Update, 3:45 p.m. ET] Paramedics were treating several victims at the scene, and police ordered onlookers to back away from the area. Troops from the Massachusetts National Guard were assisting police as well.

Onlooker Josh Matthews said he heard the blast, then saw police running toward the scene.

“We just heard a lot of sirens, and people were kind of frantic, and it was a bad situation, so we got out of there,” he said.

[Update, 3:37 p.m.] Four victims of explosions near the Boston Marathon finish line are at the emergency room at Massachusetts General Hospital, a hospital spokeswoman told CNN. She had no information about the victims’ conditions.

[Posted at 3:25 p.m. ET]

A pair of explosions rocked the finish line at the Boston Marathon on Monday afternoon, injuring at least a half-dozen people, a CNN producer at the scene said.

The blasts occurred a few seconds apart, shrouding downtown Boston’s Copley Square in smoke. Paramedics were treating several victims at the scene, and police ordered onlookers to back away from the area, CNN Producer Matt Frucci reported.

The explosions occurred about 2:45 p.m., about an hour after the first runners had crossed the finish line, Frucci said.