MANILA — The quick-thinking crew of a cargo ship thwarted a possible a hijacking or robbery at sea Saturday off Davao del Sur province by locking themselves in their quarters, the Philippine Coast Guard (PCG) said.

About eight men on two motorized outriggers boarded the MV Cecilia, but the crew quickly locked all the vessel's hatches and windows, said Commodore Joselito dela Cruz, PCG district commander on the main southern island of Mindanao.

He said the suspected pirates left empty-handed before a Coast Guard vessel arrived at the site, near Balut Island.

Dela Cruz said it was unrelated to the kidnapping last month of two Canadians, a Norwegian and a Filipino woman from Samal Island, a resort island less than 200 kilometers away.

[READ: Gunmen abduct 3 foreigners, 1 Filipino in Samal Island]

"We can say that this is an isolated incident," he said.

There has been no word on the fate of the four Samal kidnap victims.

An Italian businessman who once served as a Roman Catholic missionary also was kidnapped earlier this week in Dipolog city in Zamboanga del Norte province. No group has claimed responsibility for kidnappings, although suspicion has fallen heavily on militants from the Abu Sayyaf group which operates in the region.

[READ: Gunmen seize ex-Italian priest in Dipolog]