There were a total of 18 entrants from Singapore at the Boston Marathon on Monday, where twin explosions near the finish line have killed two and wounded more than 100 so far.

It is understood that all finished the 42.195km race before the explosions - which happened around the 4hr 9min mark - and believed to be unhurt.

Lin Run'er, a 30-year-old teacher who completed her race over four hours, said: "The explosion happened minutes after I finished and I was near the finish line.

"There were two huge cannon-like sounds and I saw smoke coming out from nearby buildings when I turned around. The race was halted and we were ushered into a shopping mall to take cover before being evacuated again."

Most of those hurt are understood to be spectators.

"Some runners didn't have their phones on them and you could see people frantically trying to reach each other," added Lin.

Melissa Keong, 37, was about 100m away from the explosions when they happened.

Said the senior solutions specialist with IT services provider Dimension Data: "When we first saw the explosion we didn't know what to think - whether it was terror or a technical fault. But when we heard the second explosion we knew it was something bigger."

The runners from Singapore had planned to gather for a post-race party.

Added Keong, who finished the race is a little under four hours: "We updated each other on Facebook to say that it's been cancelled, and hope that everyone is safe."