Two explosions close to the finish line of the Boston Marathon have killed at least 3 people, injuring more than 140.
A video shows a fireball and smoke rising from behind spectators, before the second blast just metres away.
Medics who were on hand for the finish ofthe race found themselves having to deal with those hurt in the explosions.
US President Barack Obama says those responsible will feel the "full weight of justice".
The FBI is has launched what it’s calling a "potential terrorism investigation".
More than 23-thousand runners were due to take part in the marathon, including over 100 from Ireland.
Taoiseach Enda Kenny says his thoughts and prayers are with the people of Boston.
The Irish Consulate in Boston is meanwhile providing assistance to all Irish caught up in the Boston Marathon explosions.
The Department of Foreign Affairs says if anyone is worried about a relative in Boston to call – 01 478 0822. However, officials say all of the Irish runners have been accounted for.
