SEASIDE PARK, N.J. (CBS) — Authorities say a pipe bomb exploded in a trash can near the boardwalk in Seaside Park, New Jersey as thousands of runners were getting ready to take part in a charity 5K race to benefit members of the military.

There were no reports of injuries.

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It happened around 9:30 a.m. Saturday near D Street and Ocean Avenue.

The third annual Semper Five Marine Corps Charity 5K was canceled.

Authorities immediately cleared the area near the explosion, including the boardwalk and beach.

Police said a suspicious backpack was found in the area, and there were reports of a possible second explosive device.

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The FBI, ATF and New Jersey State Police were assisting. The area was on lockdown while bomb sniffing dogs searched for additional devices.

Officials said runners had been scheduled to pass by the area around the time the blast occurred.

“Fortunately, the start of that run had been delayed because of folks coming in late to register,” Al Dellafave, a spokesman with the Ocean County Prosecutor’s Office, told CBS News.

A post on the Ocean County Prosecutor’s Office Facebook page said an arson unit was on the scene.

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The public was being encouraged to avoid the area.