Japan's unpopular prime minister reshuffled his cabinet Monday, picking a woman with Beijing-friendly credentials in what commentators said signalled his hope to move past a damaging territorial row.

Yoshihiko Noda named a relative unknown as finance minister, but kept several key positions unchanged as he seeks a balance of continuity and change ahead of an expected general election.

Noda, whose Democratic Party of Japan governs in coalition with a smaller grouping told reporters the changes would boost his government.

"This is a reshuffle that will help the government and the ruling parties cooperate to address a number of issues we are facing domestically and diplomatically and further strengthen the function of the cabinet."

Later in the day, his newly appointed ministers were formally sworn in by Emperor Akihito in a palace ceremony.

Makiko Tanaka becomes education minister. The job is relatively powerless and has little directly to do with China, but commentators say her appointment is an attempt to telegraph Noda's willingness to heal diplomatic wounds.

Japan and China have clashed repeatedly over the last few months about the Tokyo-administered Senkaku islands, which China claims as the Diaoyus.

Tanaka is the daughter of former prime minister Kakuei Tanaka, who normalised diplomatic ties with Beijing 40 years ago last Saturday, and has warm links with China, where her family is held in high regard.

She was in Beijing last week as part of a cross-party parliamentary delegation.

Her short stint as foreign minister under popular prime minister Junichiro Koizumi was marked by rows with bureaucrats. It is chiefly remembered for the tearful speech she gave after being sacked in 2002.

Noda denied her appointment was anything to do with the island spat, citing her experience in science and technology matters as vital to her new role.

"I didn't select her for foreign minister," he told reporters. "There is no way I decide on who will be education and science minister because of Japan-China issues."

However Takehiko Yamamoto, professor of international politics at Waseda University, said there was no doubt that her appointment was intended as diplomatic balm.

"This is clearly a signal and message to China, no matter what the prime minister says," he told AFP. "China considers her to be a very important person.

"Education minister is a key post that oversees cultural exchanges between Japan and China, and Tanaka is expected to improve ties from the sidelines."

Tanaka is the only female member of the cabinet and one of only a reasonably small number of women in politics in a country where gender equality lags many other developed countries.

Foreign Minister Koichiro Gemba and defence chief Satoshi Morimoto remain in post and party heavyweight Seiji Maehara is brought in to oversee national strategy, a powerful roaming brief that covers everything from fiscal policy to space matters.

Noda said he wanted Maehara "to use his ability to develop strategy for reviving Japan and to implement economic measures as commander of the entire government".

Waseda University's Yamamoto said Maehara's promotion was the flip side of Noda's decision to elevate Tanaka and was done to please party hawks.

"You cannot expect Tanaka to convince the conservative camp within the DPJ (on China) so Maehara is there to balance out her appointment," he said.

Finance Minister Jun Azumi was moved aside, with the relatively unknown Koriki Jojima taking the reins of the world's third-largest economy.

Commentators said his appointment was a strategic move by a prime minister who may soon find his legislative programme hemmed in by opposition threats to stymie parliament, including blocking a key finance bill.

Mikitaka Masuyama, professor at the National Graduate Institute for Policy Studies, said Jojima was a respected negotiator.

"Unless the bill for special bond issuance passes, the government's coffers will be empty," he said, adding that Jojima had wide experience of navigating parliament's labyrinthine party system.

The premier is under pressure to call an election this year after offering his opponents a vague pledge to dissolve parliament "sometime soon" in exchange for their support on a pet project to raise sales tax.

But woeful opinion poll numbers have left many in his factionally-riven party fearing for their seats, with the opposition Liberal Democratic Party seen likely to narrowly come out on top in a national ballot.

Japan's main opposition party chose former premier Shinzo Abe as its new leader last week, in a vote that potentially positions him to be reinstated as prime minister.