A Philippine consortium insisted Thursday a gas project in the disputed South China Sea could only work with the involvement of a Chinese firm, otherwise Beijing could make things difficult.

The Philippine government has awarded the Forum Energy consortium the exploration contract for a potentially huge gas field off Reed Bank in waters at the centre of a fierce territorial row between Manila and Beijing.

Manila accused Chinese vessels in 2011 of harassing an exploration vessel in the area, which is off the Philippine island of Palawan. The waters around Reed Bank are also claimed by China as is most of the South China Sea.

The consortium opened talks with state-run China National Offshore Oil Corp. (CNOOC) last year, and its head insisted on Thursday that it was negotiating solely with the Chinese group to be a partner in the mega-project.

"I think at the moment, the discussion would have to centre between the two of us," tycoon and consortium leader Manny Pangilinan told reporters.

"We don't want to be talking to anyone apart from CNOOC at this stage. We want to make that clear," he said, adding that it was "because of China. That is the reality we have to deal with".

He said: "I believe China will employ all sorts of tactics -- to charm you, to bully you."

He added groups, including those from the US, have expressed "soft interest" to jointly explore Reed Bank, though he stressed the inquiries were not being given serious consideration.

Pangilinan's Philex Mining group holds a 64 percent stake in Forum Energy.

Philex has said that the field is believed to hold 4.66 trillion cubic feet (TCF) of gas, nearly twice as much as the Philippines' largest known deposits.

China claims almost all of the South China Sea, including the Reed Bank, which is about 148 kilometres (92 miles) off Palawan and which the Philippines claims as its territory.

Manila has repeatedly accused Beijing of aggressive actions in disputed waters, and the two countries have been locked since last year in a standoff over the Scarborough Shoal, also in the South China Sea.