Site of Boston explosion
Site of Boston explosion Reuters

An eight-year-old boy was among those killed Monday in two explosions that hit the city of Boston. Initially reported at two, the death toll in the bombings has now risen to three after one of the wounded died in hospital.

The two bombs struck near the finish line of the Boston Marathon. Hospitals reported that at least 110 people were wounded, with at least eight of them in critical condition and 14 in serious condition, CNN reported.

At least eight of the patients are children, the report indicated.

The bombs triggered widespread screaming and chaos, shattered windows and barricades and sent smoke billowing into the air at Copley Square.

They were about 50 to 100 yards apart, officials said, according to CNN.

Photos from the scene showed people being carried away on stretchers. One man in a wheelchair had blood all over his face and legs.

The bombs shook buildings, sending people to seek shelter under tables, witnesses said.

Federal authorities are classifying the bombings as a terrorist attack, but it's not clear whether the origin was domestic or foreign, a federal law enforcement official with knowledge of the investigation said.

A federal law enforcement official told CNN that both bombs were small, and initial tests showed no C-4 or other high-grade explosive material, suggesting that the packages used in the attack were crude explosive devices.

A senior White House official, speaking on condition of anonymity, said later that "any event with multiple explosive devices -- as this appears to be -- is clearly an act of terror."

Authorities in Boston found at least one other explosive device that they were dismantling, Boston Police Commissioner Ed Davis said on Monday afternoon.

Davis said a third blast at the John F. Kennedy Presidential Library was believed to be related to the marathon bombings, but police later said that incident was believed to be fire-related. The library said all staff and visitors are safe.

It was unclear who may have planted the marathon bombs. There were no credible threats before the race, a state government official said.

There is no suspect in custody, but many people are being questioned, Davis said, though some reports indicated that authorities were guarding a person of interest at a local hospital.

The person, who sources said was 20 years old, had severe burns, but authorities had not determined whether the person was a victim or a perpetrator.

As authorities searched the scene, numerous suspicious packages were found, possibly because people fled the area, leaving items behind. Investigators were checking them.

"This is a horrific day in Boston," Massachusetts Gov. Deval Patrick said in a statement.

"My thoughts and prayers are with those who have been injured. I have been in touch with the president, Mayor (Thomas) 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," he added.

Other cities, including New York and Washington, tightened security as a result. Following standard protocol, the White House cleared out an area in front of the West Wing.

President Barack Obama said in a news conference on Monday evening that he ordered the "full resources" of the federal government to respond to the Boston bombings , though he refrained from using the word “terror” when speaking of the explosions.

"We still do not know who did this or why," the president said, cautioning people against jumping to conclusions.

"But make no mistake, we will get to the bottom of this, and we will find out who did this, we'll find out why they did this," he added.

Any individuals or groups responsible for the "senseless" bombing, said Obama, will "feel the full weight of justice."