Commander of region 1 of defense territory joint command, rear admiral Yudo Margono (front left) inspects Indonesian troops at Natuna military base in Riau islands. File photo/AFP

Indonesia has deployed fighter jets and warships to patrol islands near the disputed South China Sea, the military said Wednesday, escalating tensions with Beijing after a diplomatic spat over "trespassing" Chinese vessels.

President Joko Widodo also headed Wednesday to the fishing-rich waters around the Natuna islands, which border the South China Sea, most of which is claimed by China despite competing claims from other Southeast Asian nations including Vietnam, the Philippines and Malaysia.

The Indonesian military said it had deployed eight warships and four jet fighters ahead of Widodo's visit in an apparent bid to assert its sovereignty over the region.

A Chinese coast guard vessel was spotted near the islands Wednesday, Indonesia said.

"We have deployed eight warships," said Navy spokesman Fajar Tri Rohadi.

An AFP reporter confirmed with the air force that fighter jets had also been deployed.

It follows the deployment on Friday of around 600 personnel from the navy, army and air force to Natuna as the military launched what it called a regular patrol to secure the area due to the presence of foreign vessels in Indonesian waters.

Jakarta said it would also send hundreds of fishermen to the area to keep an eye out for foreign vessels.

The moves come after Indonesia summoned the Chinese ambassador last week and lodged a "strong protest" over a Chinese coast guard vessel escorting Chinese fishing boats around the islands in mid-December.