2 people have died and dozens have been injured in the US, after two explosive devices went off near the finish line of the Boston Marathon race.

A loud explosion was heard on the north side of Boylston Street, about three hours after the winners had crossed the line. Another thunderous explosion was heard a few seconds later. According to the Boston Globe, over 100 people are injured.

CNN confirms about 80 people are being treated in hospital. Six of them are in critical condition. US President Barack Obama has spoken to Boston governor Deval Patrick and directed his administration to provide whatever assistance was necessary.

US Federal sources have called the explosions a "well-planned event". Shortly after the blasts, a fire-related incident took place at the JFK library in Boston. The incident is believed to be unrelated to the twin explosions at the Boston Marathon.