Japan's government has agreed to buy a group of islands at the centre of a territorial dispute with China, reports said Wednesday, a move likely to prove a further irritant in a tense relationship.

Tokyo will pay private Japanese landowners 2.05 billion yen ($26 million) for three of the islands, known as Senkaku in Japan and Diaoyu in China, the Yomiuri Shimbun and Kyodo News reported, citing unnamed government sources.

Deputy Chief Cabinet secretary Hiroyuki Nagahama met the landowners on Monday and struck the deal for the islands, which includes Uotsurijima, the largest in the chain, both said.

At a news conference Chief Cabinet Secretary Osamu Fujimura refused to confirm the reports, but said negotiations were under way.

"We are exchanging views with the landowners in various ways, but that process is ongoing," he said.

"We cannot comment on the contents at all. As a government, we will make a firm announcement after procedures are appropriately completed."

The Asahi Shimbun reported that Prime Minister Yoshihiko Noda's cabinet would soon confirm the nationalisation of the islands and allocate funds for the purchase.

Noda plans to formally tell the Chinese about the purchase on the sidelines of the UN assembly later this month, the Asahi said, but a Japan-China summit has not yet been set.

The government's hand has been forced on the inflammatory issue by the outspoken nationalist governor of Tokyo Shintaro Ishihara.

Ishihara, who has made a career out of provocative remarks, often with China in his sights, earlier this year took all sides by surprise when he announced his intention to buy the archipelago for the metropolitan government.

He charges that the national government, which leases four of the five islands in the chain and owns the fifth, has not done enough to protect Japanese territory from threats by China.

Ishihara, who gathered millions of dollars of donations towards his purchase plan, had said he wanted to develop the islands and at the weekend sent a team of surveyors to nearby waters.

He told reporters on Wednesday the donations could be handed over to the national government, but said the owners had told him there was no deal as yet.

The government has no plans for any construction on the archipelago in an effort to avoid further friction with China and Taiwan, which also claims the islands, the Asahi said.

Often testy Japan-China ties took a turn for the worse in August when pro-Beijing activists landed on one of the islands, Uotsurijima. They were arrested by Japanese authorities and deported.

Days later about a dozen Japanese nationalists raised their country's flag on the same island, prompting protests in cities across China.

Last week the Japanese ambassador's car was targeted in Beijing when an unidentified man ripped the national flag off the vehicle.

Yoshinobu Yamamoto, honorary professor of international politics at the University of Tokyo, said the government's purchase of the Senkakus would make little material difference, other than to irritate Beijing.

"Practically speaking, there won't be any change in sovereignty if the islands are owned by private individuals, Tokyo or the government," he said. "This is a gesture to display Japan's effective control.''

"But I don't think it's a wise decision. It's as if Japan is picking a fight."

Yamamoto said Japan was stuck between nationalist pressure and an increasingly assertive China.

"Domestically, the decision was obviously caused by Governor Ishihara's move," he said.

"I don't think Japan can find a solution to the territorial dispute. All it can do is to maintain the status quo without enlarging the problem."

The chain, which lies on vital shipping lanes, is believed to sit on top of potentially rich gas fields.

Comprising five islands and an outcropping of rocks, it is around 2,000 kilometres (1,250 miles) from Tokyo, but less than 200 kilometres from Taiwan.