All candidates have now officially tossed their hats in the ring for the Northland by-election.

National was last, deciding on Mark Osborne over the weekend, after making a shortlist of five.

Mr Osborne says National has looked after Northland with initiatives including the Puhoi road and faster broadband - but it's not done yet.

"Obviously we're very keen to carry on and reform the RMA, we need to address the costs and delays that are holding our regions back, particularly Northland," he says.

"We really want to get on and make sure that happens."

The by-election will be held in a month.