WELLINGTON, June 17 (Reuters) - The New Zealand defence

force plane flying New Zealand's Prime Minister Christopher

Luxon to Japan broke down on Sunday, forcing the Prime Minister

to take a commercial flight, his office confirmed on Monday.

Luxon is spending four days in Japan, where he is expected

to meet with Japan's Prime Minister Fumio Kishida and spend time

promoting New Zealand business.

New Zealand media reported that the Boeing 757 broke

down during a refuelling stop in Papua New Guinea, leaving the

business delegation and journalists stranded in Port Moresby,

while Luxon flew commercial to Japan.

The New Zealand Defence Force's two 757s are more than 30

years old and their age has made them increasingly unreliable.

New Zealand Defence Minister Judith Collins told radio

station Newstalk ZB on Monday that the consistent flight issues

were "embarrassing" and that the ministry was looking at flying

Luxon and his delegation commercially from now on.

New Zealand's defence force is struggling with ageing

equipment and retaining sufficient personnel. The government has

said it would like to spend more on defence but is also trying

to reduce spending as the country faces economic headwinds.