The Government is selling its three-year-old fleet of 34 luxury limos and replacing them with new BMWs, which the Green Party says is an outrageous expense when ministers are telling everyone else to tighten their belts.

The "old" BMWs are being replaced with brand new models which are on their way to New Zealand, One News reported.

The new ones sell commercially for about $200,000 each but the Government gets a discount for bulk buying.

The total cost to the taxpayer isn't being revealed because it is commercially sensitive.

"We could go out and buy secondhand cars but one way or another cars need to be maintained and you have to renew them eventually," Finance Minister Bill English said.

The fleet is used to transport ministers and government guests, and Dog and Lemon Guide's Clive Matthew-Wilson said the Government could buy Lexus limos which did the same thing for half the price.

"The BMW Series Seven is a pre-credit crunch car," he said.

"It's from an era of bloated stockbrokers and dodgy loans and it looks completely out of place at this time in history."

A spokesman for Prime Minister John Key said it was standard commercial practise and was in line with the contract with BMW, which was first signed by the previous government.

Greens co-leader Metiria Turie said Mr Key and his ministers were always telling New Zealanders they had to tighten their belts and had said the Government was doing the same.

"When John Key is cutting staff and creating unemployment in order to apparently tighten the Government's belt, this kind of spending is an outrage," she said.