BOSTON - The anniversary of the Boston Marathon bombings has started with a wreath-laying ceremony at the site of the explosions.

The ceremony Tuesday morning was attended by the families of the three bombing victims as well as relatives of a Massachusetts Institute of Technology police officer killed in the blasts' aftermath.

Gov. Deval Patrick, Mayor Martin Walsh and Boston Cardinal Sean O'Malley were among those attending the solemn ceremony held in a light rain amid the music of bagpipes. O'Malley offered a prayer.

It was the first of what promises to be a day of tributes to those who died, the more than 260 people who were injured, and the first responders, doctors and nurses who helped them.

U.S. Vice-President Joe Biden will be among the dignitaries expected to honour the victims later Tuesday.