MANILA, Sept. 3 (Xinhua) -- An explosion broke out on Monday in a port in Masbate, an island province in the Bicol region in the Philippines, damaging Philippine army and Philippine Coast Guard (PCG) boats, but no injures were reported.

PCG spokesman Capt. Armand Balilo said the explosion occurred around 12:30 a.m. local time at Masbate port, some 100 meters away from a PCG station where the speedboats were moored.

Balilo said two new PCG boats were damaged while an army boat was totally destroyed.

"Witnesses disclosed that prior to the incident, a small motorized banca was seen roaming the vicinity of the incident," Balilo said, adding that a police investigation is underway.

According to the initial investigation, a homemade explosive was apparently used in the attack by an unknown group.

Police recovered pieces of orange polyvinyl chloride pipes and shattered pieces of the damaged boats from the site.

It was the second explosion that rocked the port in over a month. On Aug. 2, an improvised explosive device also went off at the port and damaged two motorboats owned by fishermen, police said.

No one was hurt in both incidents, police said.

Police have yet to conclude whether the two explosions are related.