Japan's Prime Minister Shinzo Abe today said his country would repel by force any attempted Chinese landing on a group of islands claimed by both nations.
His comments came as the Japanese coastguard said it has spotted eight Chinese ships sailing near the island chain in the East China Sea while conducting routine surveillance.
Tokyo has also hauled in China's ambassador to lodge a protest over Chinese ships sailing close to the islands.
The uninhabited rocky outcrops, called the Dioayu islands by China and the Senkakus by Japan, are surrounded by rich fishing grounds and are believed to harbour vast natural resources below their seabed.
The Japanese coast guard said this was the highest number of Chinese boats in the area since Tokyo nationalised part of the island chain in September 2012.
A flotilla of 10 fishing boats carrying Japanese activists was also reported to be in the area today, monitored by the Japanese coastguard.
Abe was speaking in parliament hours after dozens of lawmakers visited the controversial Yasukuni war shrine in central Tokyo, seen as a potent symbol of Japan's imperialist past, riling its neighbours China and South Korea.
A total of 168 lawmakers paid their respects at the Yasukuni Shrine, which commemorates Japan's war dead, including war criminals.
On Monday Seoul shelved a proposed trip by foreign minister Yun Byung-Se to Tokyo in protest over the weekend visits to the shrine.
China's foreign ministry spokeswoman Hua Chunying says Japan must atone for its past behaviour.
"Only by facing up to and repenting for its history of aggression can Japan create the future, and truly develop friendly and cooperative relations with its neighbours," Hua said.
But the protests did not deter more legislators visiting Yasukuni on Tuesday.
The warning from the Japanese prime minister was the most explicit to China since Abe took office in December.
Asked in parliament what he would do if Chinese ships tried to land on the disputed islands, Abe said they would be expelled by force.
"... we have made sure that if there is an instance where there is an intrusion into our territory or it seems that there could be landing on the islands then we will deal will it strongly," he said.
The territorial row has been rumbling for years but was reignited last year when Japan bought three of the islands from their private Japanese owner.
China claims the island chain, which is controlled by Japan. Taiwan also claims the islands. Chinese ships have frequently sailed around the five islands in recent months, sparking diplomatic clashes.