A Chinese fishing boat has been found stranded in the shallows of a World Heritage-listed coral reef off southern Philippines.

The small vessel ran aground on the Tubbataha Reef on Monday, coast guard spokesman Lieutenant Commander Arman Balilo told AFP.

Authorities said they were investigating how the fishing boat ended up in the protected sanctuary, roughly 1,600 kilometers (1,000 miles) from Hainan island, China’s nearest major landmass.

“Apart from illegal entry, we are investigating them for possible poaching as well,” Balilo said.

The boat, with 12 crew members, was pulled off the reef and towed to the nearby island province of Palawan on Tuesday.

Chinese fishermen frequently strayed into Philippine waters, but this was the first time in recent years that they had gone as far south as Tubbataha, Balilo said.

The Philippines and China are locked in a bitter maritime row over competing territorial claims on islands in the South China Sea.

In January, a US minesweeper ran aground on the Tubbataha, damaging at least 2,345 square meters of the reef. Philippine authorities have sought 58 million pesos ($1.4 million) in compensation.