BOSTON (CBS) - Three people are dead and more than 140 injured after two bombs went off near the Boston Marathon finish line Monday afternoon. WBZ-TV has confirmed an 8-year-old boy is among the dead.
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One explosion happened around 2:50 p.m. outside Marathon Sports on Boylston Street as thousands of runners were finishing the race. Seconds later, a second explosion occurred further up the marathon route in front of Forum, a restaurant with a patio.
There were two "incredibly powerful explosions just seconds apart," said WBZ-TV's Lisa Hughes, who was at the scene covering the marathon.
Watch: Raw Video of Explosions
Watch: Runner's Video Of Explosion
Boston Police Commissioner Ed Davis told reporters at an afternoon news conference there were "simultaneous explosions" that were about "50-to-100 yards apart."
According to CBS News correspondent Bob Orr, two bombs were inside trash cans near the viewing area close to the finish line. Two unexploded devices has been recovered intact, according to CBS News.
Orr is reporting that authorities have recovered surveillance video from the area which shows a man with what looked to be two backpacks near the scene just moments before the blast.
Commissioner Davis said there have been no arrests and that they're questioning "many people." When asked if it was a terrorist attack, Davis said "you can reach your own conclusions on that."
Federal agencies are "flooding the zone" in Boston right now, according to Orr.
Late Monday night, law enforcement officials from several agencies, including the Boston Police, were searching an apartment on Ocean Ave. in Revere, a suburb of Boston. It is not known if the search is connected to the explosions.
In an interview with WBZ-TV, Rep. Bill Keating said he had been told two more devices were found, but not detonated. One was said to be at a hotel near Copley Square, the other was at an undisclosed location.
No one has claimed responsibility and there was no advance warning.
Photos: Boston Marathon Explosions
"There was no information that this was going to happen," Davis said.
Police Search Revere Apartment
In a brief statement at the White House, President Obama said "Any individual, any responsible groups will feel the full weight of justice."
"We will find out who did this and we will hold them accountable," the president said. He did not take any questions from reporters.
Watch: President Obama Statement
The president has been in contact with Massachusetts Gov. Deval Patrick and Boston Mayor Tom Menino.
"The American people will say a prayer for Boston tonight," Mr. Obama said.
Gov. Patrick News Conference
Brigham and Women's Hospital says it's treating as many as 31 patients from ages 3 to 62 years old injured in the blast.
Dr. Peter Fagenholz says there are 29 patients being treated at Mass General Hospital and eight of them are in critical condition. He says they have performed several amputations, and most of the injuries are to the lower extremities.
There are 20 victims being treated at Beth Israel Deaconess Medical Center. Boston Medical Center is treating at least 23 patients, including two children, most of whom have received lower leg injuries and Tufts Medical is treating 12 patients.
Some people were missing limbs. Others had blood on their heads.
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A Boston University student was critically injured according to the school's president.
"There's a lot of blood" at the scene, according to WBZ-TV producer Ken Tucci, who reported seeing more than ten people taken away from the area on stretchers.
Patrick released a statement calling it a "horrific day in Boston."
"My thoughts and prayers are with those who have been injured," Patrick said.
Governor Patrick tells the people of Boston to expect a heightened police presence around the city in the next few days. He says that there will be random checks of bags and backpacks on the MBTA Tuesday.
He urges the public to be vigilant and report anything suspicious.
"I have been in touch with the President, Mayor Menino and our public safety leaders. Our focus is on making sure that the area around Copley Square is safe and secured. I am asking everyone to stay away from Copley Square and let the first responders do their jobs."
WATCH: WBZ-TV's Johnathan Elias Reporting
Several of the injured were rushed to the marathon medical tent in nearby Copley Square. Boston Police cleared out the area and the race was ended immediately.
WBZ-TV's Paul Burton was running the race at the time of the explosions. He said it sounded like cannons in the distance and then all of sudden, police were escorting all the runners off of the course.
According to WBZ-TV's Bobby Sisk, those runners were being moved to Boston Common.
WATCH: WBZ-TV's Lisa Hughes Recounts Explosions
A nurse at the finish line medical tent told WBZ-TV several children were hurt and one woman had lost a leg.
Davis said two hotlines have been set up. One is for families looking for loved ones. That number is 617-635-4500.
The other line is for anyone who may have seen anything before, during or after the explosions. That number is 1-800-494-TIPS.
WATCH: WBZ-TV Photographer Brian Foley Recounts Explosion
Davis warned everyone to stay off the streets downtown, demanding they head home or back to their hotels to be safe. Security has been increased at downtown hotels. He also asked that people not travel in groups.
A 15-block area around the crime scene has been shut down to the public until further notice.
Several runners and spectators left bags behind at the scene and along the course as they fled.
Investigators are now going through all of them, treating each as a possible suspicious device as a precaution.
The FAA said it placed a temporary flight restriction "over an area in Boston at the request of law enforcement," but the agency would not offer any specifics.
Davis said there was a third incident at the JFK Library in Dorchester around 4:20 p.m. involving an "incendiary device or a fire," but that incident does not appear to be related to the first two blasts.
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