Manila (AFP) - Nine people including four Philippine security officials were killed Tuesday during clashes with suspected Islamic militants on a popular resort island as millions prepare to travel for the Easter holiday.

The incursion allegedly by the Abu Sayyaf kidnap group on Bohol island would be the first on a key Philippine tourist destination in recent years by militants who pledged allegiance to Islamic State fighters and often targets foreigners in the lawless south.

Five gunmen were killed while four assault rifles and an improvised explosive device were recovered in the fighting, officials said.

Just days earlier the US and Australia warned their citizens about possible "terrorist" kidnappings in Bohol or nearby Cebu island. Britain on Tuesday issued a similar travel advisory.

"We're quite worried... we are afraid of hostage situations," said Khent Guimalan, who works at the upscale Bohol Beach Club.

"The mayor and police have tightened security. There's a checkpoint everywhere," Guimalan told AFP by phone from the Panglao tourist area, where she said hotels were fully booked until next week.

Following the clash authorities distributed photos of suspected Abu Sayyaf members asking locals to report any suspicious activity, according to Guimalan.

Local officials said the militants had used fast boats Monday to reach a village where they squared off against security forces early Tuesday.

- Whale sharks and tarsiers -

A Filipino photographer in the area saw a hut burning and about 20 soldiers armed with a machine gun and automatic rifles trading intermittent fire with unseen snipers all afternoon at a cornfield near the Inabanga river.

At one point, loud blasts rang out as a military plane flew over the area followed later by a helicopter, said the photographer, who asked not to be named.

He added that residents said they saw two uniformed soldiers who looked to be either dead or wounded being evacuated aboard a military helicopter.

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Security forces have been on alert for "potential activity on the part of some lawless elements" during the peak Easter tourist season, military spokesman Brigadier-General Restituto Padilla said.

"Our forces who were acting on this information were able to engage these lawless armed groups that are believed to be part of the Abu Sayyaf group from Mindanao," he said on ABS-CBN television.

The armed men sailed upriver from Inabanga, a farming and fishing coastal community some 780 kilometres away from the Abu Sayyaf stronghold of Jolo in the southern Philippines, local police told AFP.

Bohol, about 600 kilometres south of Manila, is a mere 30 minutes' boat ride away from the major port of Cebu on Cebu island, which is also among the country's top tourist draws.

The island is famous among foreign tourists who swim with docile whale sharks and marvel at tiny primates called tarsiers, go on cruises aboard boats on crystal-clear rivers and lounge on its beaches.

- Containment -

Three soldiers and one policeman were killed in the fighting, according to a joint statement from the region's military and police.

"We are doing our best to make sure the conflict will not spread out," regional army spokesman Colonel Medel Aguilar told AFP by telephone.

"We are clearing the area," said Aguilar but did not give a timetable. "We have deployed enough forces to accomplish the mission."

Bohol provincial governor Edgar Chatto said the violence was isolated in one village, where he said hundreds of residents had already fled to safety in nearby areas.

"I am very disappointed that these elements coming out of nowhere are trying to destroy the lives of people living in peace," Chatto told AFP.

The Abu Sayyaf, also blamed for deadly bombings, has pledged allegiance to the Islamic State movement that holds large swathes of Iraq and Syria.

Over the past year the Abu Sayyaf has been expanding its activities, boarding commercial and fishing vessels off their southern island stronghold of Jolo, near Malaysia, and abducting dozens of foreign crew members.

They beheaded a German tourist in February and two Canadian tourists last year. All three were snatched at sea.