New York's main contract, West Texas Intermediate crude for delivery in June, was down 94 cents to $96.14 per barrel while Brent North Sea crude for June shed 81 cents to $111.92 in morning trade.

"Weaker-than-expected Chinese trade data, higher OPEC production and evidence of a strengthening US jobs market muddied the oil demand outlook," said Phillip Futures in a market commentary.

Official customs data released Thursday showed imports in China -- the world's top energy consumer -- edged up just 0.3 percent year on year to $144.83 billion in April, raising questions about the government's ability to boost domestic demand.

China's exports to the debt-hit European Union grew a mere 0.3 percent from January to April, reflecting recent indications of a contraction in manufacturing activity.

China's weak trade performance could lead the government to loosen monetary policy to spur expansion and avoid missing annual growth targets, Phillip Futures said.

An increase in oil production by the Organisation of the Petroleum Exporting Countries (OPEC) also pressured prices, analysts said.

In its latest report, the 12-nation cartel said it pumped 31.62 million bpd (barrels per day) in April, up 0.32 million bpd from March, with Iraq, Libya, Saudi Arabia, Nigeria and Angola hiking production in a bid to stabilise prices.

Markets also remain shaken by worries about the eurozone after elections in Greece and France highlighted public rejection of austerity measures aimed at dealing with the eurozone debt crisis.

"The energy markets have been looking for some strong economic data within the European political upheaval but sadly it hasn't been forthcoming this week," said Justin Harper, market strategist at IG Markets Singapore.

The firms, which include China's biggest travel agency China International Tour Service (CITS), cited safety concerns for the suspension, just two days after Beijing said it was ready for "any escalation" in the row with Manila.

The month-long flare-up is one of the most high-profile incidents for years between the two countries over their competing territorial claims to parts of the South China Sea, which is believed to sit atop vast oil and gas deposits.

The two countries have been locked in the row since April 8, when Beijing's vessels blocked a Philippine warship from arresting crews of Chinese fishing boats near the disputed Scarborough Shoal -- or Huangyan island in Chinese.

Both Beijing and Manila claim the shoal as their own, and have since sent ships to the area that are currently facing off against each other, racking up tensions in the region.

"We stopped organising for tourists to go to the Philippines because of the current situation," an employee at the CITS Beijing branch told AFP.

China Youth Tour Service, another prominent travel agency, confirmed the suspension, saying tourism authorities had asked them to stop sending groups of tourists to the Philippines.

Another agency -- Zhongtang International Travel Service -- said it was currently "too dangerous" to send people to the country.

On Thursday an editorial in the official, English-language China Daily newspaper hinted at the possibility of war over the incident.

"No matter how willing we are to discuss the issue, the current Philippine leadership is intent on pressing us into a corner where there is no other option left but the use of arms," it said.

"Since ancient times, our nation has deemed war the last resort in handling state-to-state relations. But Manila is living in a fantasy world if it mistakes our forbearance for timidity.

"This is a dangerous delusion. We have never been a trigger-happy nation. But nor have we ever been afraid to fight when necessary."

The Philippines argues the shoal is well within the country's 200-nautical-mile exclusive economic zone, as recognised by international law.

But Beijing claims almost the whole of the South China Sea as its historical territory -- including the shoal.