At least four people were killed and more than 30 injured in twin explosions near the finish line of the Boston Marathon on Monday, police said.
Police spokeswoman Cheryl Fiandaca issued the toll via Twitter, urging all bystanders to clear the blast area.
Witnesses said the streets were littered with debris and blood and described paramedics racing off with stretchers. TV footage showed an explosion sending up a white plume of smoke along the sidelines of the race.
CNN initially reported that at least six people were wounded but later raised the toll to 30. Local radio said the first explosion took place near a sports store and the second went off near a viewing stand. Local officials could not immediately be reached.
Zara Bielkus, a 30-year-old spectator from Boston, said she heard two explosions seconds apart. Police then locked down the area.
“When we heard them, everyone looked at each other and went very quiet, and within a minute police came,” she said.
The Boston Marathon is one of the biggest annual athletic events held in the United States, with nearly 27,000 racers who must qualify to compete and tens of thousands of spectators.
President Barack Obama ordered his administration to do whatever is necessary to respond to and investigate blasts near the finish line Monday at the Boston Marathon, a US official said.
Obama was told of the incident, which caused many injuries, and the White House has been in touch with state and local authorities.