Aucklanders are being warned about closures of a major bridge in the city's west over the next four weeks

The Royal Rd overbridge over the Northwestern Motorway will be shut most nights for a month, from tonight.

The closures will happen from 8pm to 5am, Sunday to Thursday - dependent on the weather.

NZTA says the bridge has greater height clearance over the motorway than the one it replaced.

It says the closures are to allow the road on the eastern side and the on-ramp to the motorway to be built up to the same height as the bridge.