The youngest victim of yesterday's terrorist attack on the Boston Marathon has been named as eight-year-old Martin Richard.

Martin was waiting with his mother and sisters for his dad, Bill, to complete the race when two bombs went off close to the finish line, causing panic and destruction.

While Martin died in the attack, his mother Denise and one of his sisters suffered major injuries and are receiving treatment at a local hospital.

A solitary candle has been lit outside the Richards' family house in the Boston suburb of Dorchester in memory of the young victim.

More than 140 people were injured in yesterday's bombings, 17 critically. At least eight children were being treated at local hospitals.

At least 10 people had to undergo medical amputation because of the wounds suffered in the blast, the CNN reported. Among them were two brothers, who lost one leg each.

Liz Norden, from the suburb of Wakefield, told the Boston Globe she received a call in the aftermath of the attack from one of her sons, who told her he was being driven to the Beth Israel Deaconess Medical Center by ambulance.

The 31-year-old son said he was badly injured and had lost contact with his older brother, 33, who was sitting beside him near the end of the 26.2-mile (42km) course when the bombs went off.

The woman, who didn't want to name her injured sons, traced down the elder one, who had been taken to a different hospital. Both had had a leg amputated from the knee down.

"I'd never imagined in my wildest dreams this would ­ever happen," Norden told the Globe. "I feel sick, I think I could pass out."

No group has yet claimed responsibility for the bombings.

A Saudi national, who was being kept under guard at a Boston hospital, is reportedly cooperating with investigators and told agents he was not involved in the blast.

The man is reportedly a 20-year-old local university student and told FBI he ran from the scene because he was frightened. Investigators have specified he is not in custody and is not being described as a suspect.

Anyone with information about the explosions is urged to call +1-1800-494-TIPS.

Boston Bombing
Agents arrive on scene after explosions near the finish line of the Boston Marathon (Reuters)