Tokyo summoned China's envoy Tuesday in protest at what it says was another incursion into its territorial waters, after Beijing's ships sailed near islands at the centre of a bitter dispute.

"The foreign ministry summoned the Chinese ambassador over ships entering the waters near Senkaku islands," said an official, referring to a chain claimed as the Diaoyus by Beijing.

The move comes after Chinese state vessels spent much of Monday in waters around the islands and as the two sides show no sign of backing down in a dispute that has badly affected trade between Asia's two largest economies.

Two maritime surveillance boats arrived in the area shortly before 9:30 am (0130 GMT), the Japanese coastguard said, adding that they had remained there for around 14 hours.

Chief Cabinet Secretary Yoshihide Suga told a news conference the actions were "absolutely unacceptable", adding Ambassador Cheng Yonghua had been called to the foreign ministry to hear Japan's "strong protest".

Chinese ships have repeatedly ventured into the waters, in what observers say is Beijing's bid to create a "new normal" in which Tokyo does not have effective control over the archipelago.

A Chinese government plane entered the chain's airspace in December, setting off sorties by Japanese fighter jets.

In recent weeks both countries have dispatched military planes, which on at least one occasion have shadowed each other, although there have been no clashes.

But analysts say the ramping up of rhetoric and the more frequent confrontations raise the risk of an accidental armed conflict.

On a Saturday visit to Okinawa, Prime Minister Shinzo Abe vowed to defend Japan against "provocations", just days after his government approved a rise in defence spending for the first time in over a decade.

Some of the cash is earmarked for beefing up defence of the contested island chain in the East China Sea.

"Provocations are continuing against our country's inherent territorial land, air and sea as well as its sovereignty," Abe told troops in the island's capital, Naha, in an apparent reference to China.

Japan's already well-equipped coastguard said last week it would create a special unit over three years with 10 new large patrol boats, two helicopter carriers and a 600-strong force to oversee Japanese territory in the East China Sea.

Abe, who swept to power in an electoral demolition of his centre-left opponents, has made much of his muscular diplomatic credentials.

In the run up to December's poll, he talked tough on China and the need for Japan to stand up to what he and other politicians in the region say is a sometimes-domineering Beijing.

After taking office, he embarked on a three-country tour as part of a bid to shore up alliances in South East Asia.

But his tough talk has been matched with apparent olive branches offered to Beijing. In a television interview he suggested China and Japan needed to hold a summit and has sent two emissaries to Beijing in recent weeks.