(AP) -- A pipe bomb exploded in a Jersey Shore town Saturday shortly before thousands of runners were due to participate in a charity 5K race to benefit Marines and sailors, authorities said.

No injuries were reported in the blast in Seaside Park around 9:30 a.m. Saturday, said Al Della Fave, spokesman for the Ocean County Prosecutor's office. He said no surrounding structures suffered any apparent damage, as well.

Investigators would not say if they suspected participants in the third annual Semper Five run were targeted. The race was canceled, and the immediate area was put on lockdown.

The pipe bomb was in a plastic garbage can when it exploded, Della Fave said. Authorities immediately cleared the boardwalk and beach area, and bomb-sniffing dogs were used to search the area.

New Jersey State Police said later in the day that bomb technicians "rendered safe" items located in a plastic trash can where the explosion occurred; they did not specify what those items were or provide further details. They also said there was nothing to reports of another explosive device near the site of the explosion.

Officials said runners had been scheduled to pass by the area around the time the blast occurred. But the start of the race had been delayed after an unattended backpack was found, and the area was mostly empty when the bomb went off.

Numerous state and federal law enforcement agencies were investigating. Attorney General Christopher Porrino and Col. Rick Fuentes, superintendent of the state police, briefed Gov. Chris Christie on the investigation.

"Working with the FBI and ATF, we are taking every step to ensure the safety of the public and to determine who was responsible for this explosion, which occurred at a time when runners in this charity race could have been in harm's way," Porrino said in a statement. "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."

It wasn't clear when the boardwalk and beach would reopen. Other community events went on as planned in nearby towns on Saturday, though officials said security at those sites had been stepped up in the wake of the blast.

Some homes near the scene were evacuated as a precaution, and the public was being urged to avoid the area.

It wasn't immediately clear if the charity race would be rescheduled.