Manila, Apr 5 (IANS): Philippine President Rodrigo Duterte has threatened to send his troops on a "suicide mission" if Beijing doesn't "lay off" a Manila-occupied island in the South China Sea, the media reported on Friday.

Duterte's speech at a rally in the city of Puerto Princesa in Palawan came days after the Philippine government claimed as many as 275 Chinese boats and ships had been spotted in recent months around Manila's Thitu Island in the Spratly Island chain, CNN reported.

"Let us be friends, but do not touch Pagasa Island and the rest," Duterte said using the Philippine word Pagasa for Thitu.

"If you make moves there, that's a different story. I will tell my soldiers, 'Prepare for suicide mission'."

Duterte said his words were not a warning, but rather "advice to my friends".

"I will not plead or beg, but I'm just telling you that lay off the Pagasa because I have soldiers there," he said, according to CNN Philippines.

A small Philippine military garrison as well as about 100 civilians are based on Thitu, which lies about 500 km from Palawan, one of the islands that make up the Philippines.

Tensions have risen since the start of 2019 in the South China Sea, one of the world's most disputed regions and an important shipping lane.

The Philippines and China each claim overlapping areas of the vast sea, along with multiple other countries including Vietnam, Malaysia and Brunei. The area where Thitu is located is also claimed by China as part of its territory.

The latest arrival of Chinese vessels around Thitu Island has provoked a stern response from Manila.

The Philippines Department of Foreign Affairs in a statement Thursday said their presence was "illegal" and a "clear violation of Philippine sovereignty".