Two people are reported dead and 22 were injured after two explosions at the finish line of the Boston marathon about three hours after the winners crossed the line
TV footage showed emergency workers treating people at the scene. One report said the explosion came from a sports shop near the Fairmount Copley Plaza Hotel.
"There was an explosion, police, fire and EMS are on the scene. We have no indication of how many people are injured," a spokeswoman for the Boston Police Department said.
The explosion occurred as thousands of runners finished the 117th running of the Boston Marathon, with crowds watching and cheering at the finish.
"There are a lot of people down," said one man, whose bib number 17528 identified him as Frank Deruyter. He was not injured, but marathon workers were carrying one woman, who did not appear to be a runner, to the medical area as blood gushed from her leg.
Mike Mitchell of Vancouver, Canada, a runner who had finished the race said he was looking back at the finish line and saw a "massive explosion." Smoke rose 50 feet (15 metres) in the air, Mitchell said. People began running and screaming after hearing the noise, Mitchell said. "Everybody freaked out," Mitchell said.
A Boston police officer was wheeled from the course with a leg injury that was bleeding.
Massachusetts General Hospital is treating four victims of the explosions near the Boston Marathon finish line, said Ryan Donovan, a spokesman for the hospital. Mr Donovan said he didn't have information about the severity of the injuries or whether there were any fatalities
The New York Police Department has stepped up security around landmarks in Manhattan, including near prominent hotels following the explosion, said Paul Browne, deputy commissioner of the NYPD.
He said New York police were re-deploying counter-terrorism vehicles around the city.
More to follow...