Japan will request a record defence budget next year amid growing worries over North Korea and tensions with China, reports said Friday.

The defence ministry has decided to seek 5.168 trillion yen ($51.5 billion) in spending for the fiscal year starting April 2017, up 2.3 percent from this year's initial budget, Jiji Press reported, citing unnamed government sources.

If approved by parliament, the budget package would mark the fifth straight increase and a new record, it said.

Top business daily Nikkei and other media also carried similar reports, which a defence ministry spokesman said he could not confirm.

The budget plan includes strengthening Japan's ballistic missile defence system, following missile launches by North Korea this year, the reports said.

It also includes plans for a new land-to-sea missile as part of moves to beef up the defence of Japan's remote southern islands, the reports said.

Those include populated ones as well as the uninhabited Senkaku chain, claimed by China which calls it Diaoyu.

The top selling Yomiuri Shimbun daily reported earlier this week that Japan plans to develop a new land-to-sea missile with a range of 300 kilometres (190 miles), far enough to reach the vicinity of the disputed islands.

Friday's reports come two days after Japan lodged a fresh diplomatic protest against China, accusing it of again sending coast guard ships into waters surrounding the disputed, but Tokyo-controlled, islands in the East China Sea.

The two countries are locked in a long-running dispute over the islets and ships of the two countries regularly play cat and mouse in the waters.

China is also involved in maritime disputes in the South China Sea and it reacted angrily last month to a UN-backed tribunal ruling that its claims over most of the vital trade artery were invalid.