Yoshihiko Noda, Japan's prime minister, has reshuffled his cabinet, bowing to opposition pressure for ministerial scalps as he looks to secure cross-party support for a sales tax increase.

Noda on Monday announced a limited rejig naming five new ministers and called on the Liberal Democratic Party (LDP) to give their backing to a bill that would eventually double sales tax and help partially plug a gaping budgetary hole.

"I decided to reshuffle and strengthen the cabinet so as to create an environment that enables progress in issues including an overall reform of social security and tax," Noda told reporters.

Noda has staked his premiership on the sales tax, which would bring it to 10 per cent by 2015 from five per cent now.

International bodies, academics and journalists all agree the raise is a sensible measure in the battle to overhaul Japan's debt mountain, which currently stands at about twice GDP.

Part of the proceeds would be used to finance spiralling social security costs resulting from Japan's rapidly ageing society.

But in the highly factionalised world of Japanese politics, Noda has been left trying to placate an opportunist opposition after failing to secure the backing of one of his own party's key powerbrokers.

Democratic Party of Japan powerbroker Ichiro Ozawa, who leads a bloc of about 100 members of parliament, has set his stall firmly against the tax rise, which he sees as politically unacceptable.

Some of Monday's sackings were part of the price Noda must pay if he wants cross-party backing for his bill.

'Crucial decision'

"Toward the end of the current parliamentary session, we will face a crucial decision that will affect the future of Japan," he said.

"I call for all the politicians, on both sides of the house, to take these proposals seriously," he said, adding the bill would come before the lower house before the parliamentary session ends on June 21.

The latest reshuffle comes after defence minister Naoki Tanaka and transport minister Takeshi Maeda lost their jobs after both being censured by the opposition-controlled upper house in April.

Noda named Takushoku University professor Satoshi Morimoto, a well-known polemicist and regular on television talk shows, as new defence minister, while the new transport minister will be his party's upper house affairs chief Yuichiro Hata.

Morimoto is the first non-parliamentarian in a Noda cabinet. An advocate of a closer security alliance with the United States, Morimoto has said Japan's armed forces should actively participate in peacekeeping missions abroad, once a sensitive issue in Japan.

Noda also sacked agriculture minister Michihiko Kano, whose involvement - albeit at several steps removed - in a spy scandal that allegedly saw sensitive documents passed to a Chinese diplomat, has proved an embarrassment.

Justice minister Toshio Ogawa, who has been criticised by the LDP for consulting horse racing websites on his mobile phone during a parliamentary session, and postal services Minister Shozaburo Jimi were also removed.

Noda named former vice agriculture minister Akira Gunji as new agriculture minister, vice judicial affairs minister Makoto Taki as justice minister, and vice reconstruction minister Tadahiro Matsushita as postal services minister.

Noda stressed Monday that "making an agreement with the largest opposition LDP is the most important" thing in enacting a tax rise bill, but stopped short of offering the opposition any kind of grand coalition.