Two bomb blasts ripped through spectators and competitors near the finish line of one of the sport's iconic events.

Sheridan was at home in Newcastle when news of the tragedy reached Australia.

Mum Heather Rosconi said her daughter was still too rattled to speak about the terrorist attack.

"We spoke to her very early this morning after she had spoken with Kurt," Mrs Rosconi said.

"She was very shaken at the time but we have spoken with her since and she seems a bit calmer.

"Everyone in the sport has been rocked by this, but it's not just the athletes who are devastated.

"You just don't expect something like this to happen at a sporting event."

Mrs Rosconi said when Kurt called the family he said he had finished a couple of hours earlier and was having lunch nearby when the bombs went off.

She said from what she understands, the attack appears to have been timed for when the greatest number of competitors were crossing the finish line, including those groups who were running in support of charities. 

At least three people are dead and close to 100 people have been injured - many have lost limbs. 

Mrs Rosconi said the tragedy occurred on Patriots Day, with the marathon in the morning and a Red Sox game set down for the afternoon.

Patriots' Day is a Massachusetts state holiday commemorating the opening battle of the American Revolution.

Commentators are already starting speculate on the possible significance of the holiday in relation to the bombings. 

She said while Kurt was not in any danger, he was close enough to know what was going on. He knew his family would be frantic.

"Most of the time Sheridan stays at home when Kurt is competing because she has her own work to do," Mrs Rosconi said.

"Every now and then, when she can arrange a bit of time off, she will go with him - especially to big events like the Paralympics.

"What we are really worried about now is that Kurt, along with many others, will be going straight onto London to compete in the London Marathon which has been promoted this year as a kind of double header with the Boston Marathon.

"That is on top of the fact that there is already unrest in London because of Margaret Thatcher's funeral."