Image copyright Getty Images Image caption State and federal law enforcement agencies are investigating the explosion

A pipe bomb has exploded on the route of a road race in the US state of New Jersey, forcing the event to be cancelled but causing no injuries.

The bomb had been placed in a rubbish bin along the route of the 5km Semper Five run in Seaside Park.

The participants would have been in the area but the race had been delayed because of an unattended bag.

The charity race, in its third year, is in aid of Marines and sailors and this year attracted thousands of runners.

'Serious act of violence'

The blast occurred at about 09:30 local time (13:30 GMT) on a boardwalk area, which authorities sealed off.

State and federal law enforcement agencies are investigating the explosion.

NBC reported that a second device had been found. Ocean County sheriffs said that 30 homes near the site of the explosion were evacuated.

New Jersey State Police later said that no further explosive devices had been found, although officers "rendered safe" items in another rubbish bin, without giving further details.

Attorney General Christopher Porrino said: "We are grateful that nobody was injured, but this is a serious act of violence against the people of New Jersey. We will not rest until we find the person or persons responsible."

Three people were killed and 260 injured when bombs exploded at the finishing line of the Boston Marathon in 2013.