Japanese Prime Minister Shinzo Abe on Wednesday visited coastguards who patrol waters around islands at the centre of a dispute with China, as election campaigning stepped up a gear.

Abe was in the remote Okinawan island of Ishigaki in the East China Sea, 2,000 kilometres (1,240 miles) southwest of Tokyo, where he told crews his resolve to stand up for Japan was undimmed.

"The security environment for our territorial waters has become increasingly serious, as Chinese government ships frequently sail to and roam around waters surrounding Senkaku islands," Abe said in an address to about 40 coastguards.

Senkaku is Japan's name for islands it controls, but which China claims as the Diaoyus.

"I very much appreciate your efforts to patrol our territorial waters. I will continue to take charge and defend our territory, territorial waters and territorial airspace," said Abe, who wore a blue Okinawan shirt and a coastguard cap for the occasion.

Abe's visit to Ishigaki, which lies less than 200 kilometres off the coast of Taiwan, was the first by a sitting premier in 48 years, national broadcaster NHK said.

It comes as the dispute with Beijing over the sovereignty the uninhabited, but resource-rich islands further north continues to fester, with little sign of any improvement in sight.

"The Senkakus are undoubtedly an integral part of Japan, historically and under international law," Abe said in Ishigaki later in the day.

"We won't budge one bit," he said in a stump speech.

The visit comes just a few days ahead of elections for half of the seats in the upper house of parliament, which observers expect to be a shoo-in for Abe's Liberal Democratic Party.

Voters have warmed to his economic policies, although many remain wary of his stance on issues including Japan's warring past and his intention to change the country's pacifist constitution or strengthen its armed forces.

Since taking office in December, Abe has visited a number of foreign countries, but has stayed away from China, with whom relations remain more-than-usually prickly.

Tensions have steadily risen between the two Asian giants, with China frequently sending official ships into waters around the Tokyo-administered islands.

Vessels from the two countries have for months traded warnings over intrusions into what both regard as their sovereign areas around the islands.

The long-standing dispute reignited last September when Tokyo nationalised three islands in the chain in what it said was a mere administrative change of ownership from a private landowner.

China insists the islands were part of its territory until Japan annexed them in 1895.