SEASIDE PARK — A military charity race was canceled Saturday morning the borough placed on lockdown after a bomb in a trash can exploded on the route of the Semper 5K run.

The Ocean County Prosecutor's Office said bomb dogs are searching for a possible second device in Seaside Park.

The reason or cause of the explosion was not immediately known Saturday morning, but a spokesman for the prosecutor said the device was not a "prank" and the New York City Police Department's Counterterrorism Bureau said it was "closely monitoring" the investigation.

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The device exploded before the race started and there were no reported injuries.

In the meantime, authorities were asking people to avoid the borough as the investigation continues.Ocean County Sheriff Mike Mastronardy said traffic into Seaside Park was closed as of 12:45 p.m. along Ocean Avenue, including Central Avenue between 9th Street and I Street.

The explosion prompted other Jersey Shore towns to sweep public trash cans and add security to their own events or cancel them altogether. The boardwalk in neighboring Seaside Heights, however, remains open.

“We had a device go off at D and Ocean," Mastronardy said. "Right now we are making sure there are no injuries. EMS and fire was here as a precaution. Right now everything is under control. We’re just clearing the area and making sure it’s safe."

Mastronardy said a suspicious backpack checked out as being OK.

K9 units and the Ocean County and State Police bomb squads were being brought in as part of a sweep of the area.

The Festival of the Sea in Point Pleasant Beach, was canceled after a search by police.

Belmar Mayor Matt Doherty said the area along Main Street for his town's Feast of San Gennaro was getting added security.

"We are adding on additional police and security. All our garbage cans have been checked. They'll all be brought in overnight and be put out again in the morning," Doherty said.

New Jersey 101.5 reporter Dianne DeOliveira, who was participating in the race, said the explosive went off as a "fun run" for kids was ending around 9:30 a.m. She said everyone was directed to go toward the Boulevard. She said everyone who parked in the lot along Ocean Boulevard was not allowed to get to their cars.

The event's organizers on their Facebook page thanked police and first responders for their quick action.

"The safety and security of our participants, spectators, staff and volunteers is of utmost importance. We'd like to thank the Seaside Park Police Department, all the first responders and emergency personnel for their quick action. Further details will be posted when available," they said in a statement.

Townsquare Media's 105.7 The Hawk, which was broadcasting from the event, was ordered to leave their studio on the boardwalk.

The Seaside Park race benefits the MARSOC Foundation, which provides benevolent support to active duty and medically retired MARSOC personnel and their families as well as to the families of Marines and sailors who have lost their lives in service.

Tom Mongelli, Dianne DeOliveira and Brian Gregory contributed to this report