Hundreds of Marines quickly joined the search for Vinciguerra, 47, and Dutchman Ewold Horn, 52, who were seized by armed men on a tiny island in the lawless south of the country on Wednesday.

“There is a massive search-and-rescue operation right now to find the kidnappers and their captives,” regional military spokesman Lieutenant Colonel Randolph Cabangbang told AFP.

“Though, as of the moment, we have not pinpointed their exact location.”

Cabangbang said it remained unclear who abducted the men, but noted a spate of other kidnappings of foreigners in the south that were blamed on the Al-Qaeda-linked Abu Sayyaf group.

“We cannot rule out the possibility that the Abu Sayyaf is involved,” he said. “However, I must stress there are other armed groups, including pirates, who also operate in these waters.”

Ivan Sarenas, a Filipino guide for the two wildlife enthusiasts, was also kidnapped, but said he managed to jump off a boat that was taking the abducted men away.

“There was a passing boat and I decided to go for it. I held the barrel of the long firearm of the man in front of me with one arm and jumped out,” he told AFP by phone.

Cabangbang said the first 24 hours were crucial in deciding the fate of people kidnapped in the area because this was when they were typically taken into the abductors’ rugged jungle lairs on remote islands.

“If the trail goes cold, the chances of recovering them swiftly will vanish little by little,” he said.

At least 10 other foreigners have been kidnapped in the south since the middle of 2010, in what is largely a ransom business with the Islamic militants demanding huge amounts of money for their captives’ release.

Five of those kidnapped — an Australian, two Malaysian traders, an Indian married to a Filipina and a Japanese man — remain in captivity.

Over the past decade, dozens of foreigners and locals have been kidnapped. Some of them, including an American, were beheaded after ransoms were not paid.

Sarenas said the trio were kidnapped while on an expedition to photograph extremely rare pigeon and hornbill species on the Tawi Tawi islands, which are in the Sulu Sea, closer to Malaysian Borneo than major Philippine landmass.

“They are both into hornbills and they told me they wanted to see the rarest ones before they grew old,” Sarenas said.

Sarenas is a member of the Wild Bird Club of the Philippines and officials with the organisation said information they had received indicated the foreigners were initially abducted by locals and not well-known militants.

“They apparently planned to sell them (the hostages) to the Abu Sayyaf or the MILF,” club treasurer Michael Lu told AFP.

The 12,000-strong MILF, or Moro Islamic Liberation Front, is the country’s largest Muslim separatist rebel group but is now in peace talks with the government.

In the local kidnapping-for-ransom business, it is common for small abduction gangs to “sell” their captives to more powerful organisations such as the Abu Sayyaf.

A rotating force of 600 US troops has been stationed in the southern region of Mindanao for a decade, helping to train local soldiers how to combat the Abu Sayyaf and other Islamic militants.

But the militants have remained a threat, partly because of their ability to raise funds through kidnapping-for-ransom operations. The Abu Sayyaf is believed to have just a few hundred militants.