Japan plans to buy 105 US-made stealth warplanes, US President Donald Trump said today.

Japan plans to buy 105 US-made stealth warplanes, Donald Trump said on Monday, which the US President said would give Tokyo the largest F35 fleet of any US ally.

Trump, in Tokyo for a state visit, said Japan "has just announced its intent to purchase 105 brand new F35 stealth aircraft. Stealth, because, the fact is you can't see them."

"This purchase would give Japan the largest F35 fleet of any US ally," added the president.

Trump appeared to be referencing a deal first announced by the F35's manufacturer, Lockheed Martin, in December.

Japan's government announced in its latest defence budget in December plans to buy 105 units of the F35A, which performs conventional take-off and landings.

Local media said at the time that the purchases could total more than one trillion yen ($9.1 billion).

The White House could not immediately comment on the timing of Trump's comments about the deal Monday.