The Philippines on Friday urged China to be a "responsible" power, while expressing concern again over the Asian giant's increasing assertiveness in disputed waters.

Tensions in the strategic and resource-rich South China Sea have escalated in recent weeks, with the Philippines and Vietnam voicing alarm at what they say are increasingly forceful Chinese actions there.

Foreign Secretary Albert del Rosario said he did not expect rival sea claims to lead to armed conflict but he planned to visit China next week and looked forward to discussing the dispute with Chinese leaders.

"We're counting on China's rise and growth and progress as being a responsible one," del Rosario told reporters.

"I have been invited to go to Beijing and I'm sure we will be looking for peaceful means to be able to settle the challenges that appear to be facing us."

Del Rosario said his trip to China was tentatively set for July 7-9, although the dates had yet to be confirmed.

He also indicated that Philippine President Benigno Aquino would eventually accept a longstanding invitation by the Chinese to visit, although that trip was also unconfirmed.

"We're still trying to discuss the (Aquino) China trip," he said.

Del Rosario repeated Philippine accusations of Chinese forces opening fire on Filipino fishermen, shadowing an oil exploration vessel employed by a Filipino firm, and putting up structures in areas claimed by the Philippines.

He said he did not know why China had suddenly become more aggressive.

"I can only speculate that there appears to be some finding of significant natural gas deposits in the area," he said.

Defence Secretary Voltaire Gazmin also expressed concern Friday over the Chinese actions, which he said was forcing the ill-equipped Philippine military to re-evaluate its priorities.

"The truth of the matter is that there were violations that were noted during this period, and we find the increase in intrusions very alarming," he told reporters.

"Before, we were giving high priority to internal security operations, but lately it appears that the equation had changed because we have many deficiencies that have to be addressed immediately."

Gazmin said fighter planes were now a higher priority, six years after the Philippines retired the last of its Vietnam War-vintage F5 fighter jets.

Air force spokesman Lieutenant-Colonel Miguel Ernesto Okol said the country was looking to acquire between four and six fighter jets before 2016 for air defence.

"It should be a multi-capable aircraft (that) can also perform other missions like maritime patrol, limited interceptions, and if necessary to chase after targets," he said.

But Okol said there were no firm plans yet for the cash-strapped Philippine military to buy the jets.