The two explosions that rocked the Boston Marathon on Monday has killed three people and injured at least 138, officials and media outlets said.

Local police said the death toll has risen to three, including an 8-year-old boy, according to CNN. At least 17 injured were in critical condition and 10 need to carry out amputations.

The twin explosions happened at around 3 p.m. local time (1900 GMT) and went off within seconds of each other near the Boston Marathon finish line. Many of the injured appeared to be spectators who had gathered at the scene, local media WCVB.com reported.

A FBI official told a press conference in Boston that a criminal investigation has been launched, which has a potential to be a terrorist probe.