The Philippines and China traded fresh accusations Tuesday of illegal incursions in a disputed area of the South China Sea, while refusing to compromise on their territorial claims.

The Philippines said it had lodged a new diplomatic protest, accusing Chinese vessels of harassing a Filipino-flagged archaeological research ship at Scarborough Shoal.

The shoal is the same area where Chinese vessels last week blocked a Filipino warship from arresting the crews of eight Chinese fishing boats.

Department of Foreign Affairs spokesman Raul Hernandez said the M/Y Saranggani was "harassed by Chinese ships and aircraft" at Scarborough, which is about 230 kilometres (140 miles) from the Philippines' main island of Luzon.

"We lodged the protest yesterday afternoon. The harassment of the vessel is part of the continued intrusion and illegal activities being done by China in our area," Hernandez told AFP.

Philippine National Museum director Jeremy Barns said the vessel was conducting a preliminary survey of potential ancient shipwrecks, and was manned by Filipino and French scientists, including nine French archaeologists.

"We're looking for the wrecks of Western as well as Asian vessels -- Vietnamese, Thai, and also Chinese. This is a project of the National Museum," Barns told AFP.

He described the area around the shoal as an important maritime passageway for foreign vessels that conducted trade with the Philippine islands, possibly even prior to their colonisation by Spain in the 16th Century.

Filipino officials would not say when the scientific vessel specifically arrived in the area, but Hernandez said the boat was still there.

"It is doing research, which is well within our rights," he said.

But the spokesman for the Chinese embassy in Manila, Zhang Hua, insisted China owned Scarborough, and accused the Saranggani of intrusion.

"We urge the archaeological vessel leave the area immediately," Chang said in a statement.

China claims all of the South China Sea as its own on historical grounds, even waters approaching the coasts of the Philippines and other Southeast Asian countries.

The nearest Chinese land mass from Scarborough Shoal is Hainan province, 1,200 kilometres, (750 miles) to the northwest, according to Philippine naval maps given to the media.

The rival claims have been a source of regional tensions for decades, and the Philippines as well as Vietnam have accused China over the past year of becoming increasingly aggressive in asserting its position.

The latest flare-up occurred on April 8 when the Philippines found the eight Chinese fishing boats at Scarborough Shoal, and sent its warship to arrest the crew.

China quickly deployed three civilian maritime vessels that took turns in blocking the warship.

In a bid to calm the situation, the Philippines pulled back its warship and replaced it with a coast guard vessel late last week, and the fishing vessels sailed away over the weekend.

Hernandez said a lone Philippine coast guard boat now remained in the area on Tuesday, facing off against two Chinese civilian ships.

"As of now, we are still in a stalemate or a stand off," Hernandez said. cgm/jvg/kma/emb