BRITISH runners described how they avoided being caught up in the deadly explosions by a matter of minutes.
Some 347 of the 25,000 taking part in the race were British and several told of the aftermath of the two blasts.
Abi Griffiths, from London, crossed the finishing line around 10 minutes before the "chaos".
The 34-year-old told Sky News she heard the explosion while collecting her bag.
"The ground shook and immediately people sort of looked around - it was just too loud to be something that wasn’t serious," she said.
"People kind of didn’t know what to do. Then all of a sudden it went into a state of chaos.
"Police were everywhere, we were being evacuated out of the area and it was really eerie.
"It was very, very scary and what should be a major celebration of the achievement of running 26.2 miles suddenly became a frightening scene."
She said police had swung into action quickly.
"This is just such an awful scene to have happened," Ms Griffiths continued. "It felt like it may have come from the inside of a shop.
"Suddenly you looked around and there was this cloud of smoke and then people went into gear. There were police everywhere."
Jez Hughes, a firefighter from Morley, west Yorkshire, was walking to the subway with his wife when they heard two explosions.Related content
He had been standing only 100 yards from the finish line with other competitors after completing his 10th marathon but walked around the corner to meet his wife.
"While we were going to the subway we heard two explosions. I said straight away that sounds like a bomb and then we heard a second one," Mr Hughes, who was running for The Fire Fighters Charity, said.
"My wife is very shook up but we are out here until Thursday evening and no terrorists are going to spoil our day, don’t let them get the better of you.
Darren Foy, 40, from Southampton, his wife Sandra and their two children, missed the explosions by just half an hour after he finished the marathon in three and a half hours.
The chartered surveyor, who is chairman of the Lordshill Road Runners in Southampton and was competing in his fourth marathon, said: "There are reports here that the explosions came from a hotel at the finish line and I walked past there a few days ago to pick up my race number.
"It’s such a soft target. There are hundreds of thousands spectators on the streets and 27,000 runners, so we got off lightly."
Mark Jenkin, a 34-year-old sports writer from Barnstaple in Devon, said the explosion had put the race into perspective.
After finishing 138th in a time of 2 hours 24 minutes, he told his paper, the North Devon Journal: "It’s a beautiful spring afternoon in Boston. The people of the city put on a great race and it’s such a tragedy this has happened.
"I was feeling tired and a bit disappointed with my time in the race but all that seems irrelevant now. I just feel grateful to be ok."