A Chinese vessel has locked its weapon-targeting radar on a Japanese ship, Tokyo says, amid mounting tensions over a territorial row.

According to BBC News, Japanese Defense Minister Itsunori Onodera said the incident happened on Jan 30 near islands claimed by both nations in the East China Sea.

He said this prompted Tokyo to lodge a formal protest with Beijing on Tuesday.

The row, over islands known as Senkaku in Japan and Diaoyu in China, has escalated in recent months.

"On January 30, something like fire-control radar was directed at a Japan Self-Defense Maritime escort ship in the East China Sea," Onodera told reporters on Tuesday.

The minister added that a Japanese military helicopter was also targeted with a similar radar a few days earlier.

"Directing such radar is very abnormal. We recognize it would create a very dangerous situation if a single misstep occurred," he said.

China has so far made no official comments on the issue.

The dispute over their ownership of the islands has been rumbling for years, but it reignited in 2012 when the Japanese government purchased three of the islands from their private, Japanese owner.