President Rodrigo Duterte said Tuesday he has asked China to send sea patrols to help stop Islamic militants abducting sailors and attacking vessels off the southern Philippines.

Duterte said he would like Beijing to dispatch a fleet like it did in 2009 when it sent a naval convoy to the Gulf of Aden to protect Chinese ships from Somali pirates.

"I also asked China if they can patrol the international waters without necessarily intruding into the territorial waters of countries," Duterte said in a speech to newly promoted Filipino generals.

"Grey ships are not really needed," he said, an apparent reference to warships.

"I said even coast guard cutters would do, just to patrol, like what they did in Somalia."

Manila has said militant groups are trying to establish an Islamic State-backed caliphate in Southeast Asia that would include the Philippines' southern island of Mindanao.

Duterte pointedly made his appeal for help to China rather than the United States, which has traditionally been the country's main defence ally.

Since his election last year, Duterte has responded to US criticism of his deadly war on crime by pivoting away from America and moving closer to China, despite ongoing territorial disputes between the two.

Abu Sayyaf, one of the groups seeking to set up a caliphate, began kidnapping sailors in waters between Malaysia, Indonesia and the Philippines last year, taking several dozen hostages and attacking cargo ships.

Indonesia has warned the region could become the "next Somalia" and the three later pledged coordinated patrols.

The International Maritime Bureau said this month the number of maritime kidnappings hit a 10-year high in 2016, with waters off the southern Philippines becoming increasingly dangerous.