A rescue operation is underway for a tramper missing on the Milford Track since Sunday. 

Police say despite extensive searching on Monday, the man has not been found. 

The tramper is experienced in the outdoors, they said. 

The search was scaled-up during the day, with a specialist Alpine Cliff Rescue (ACR) team from Queenstown joining the search, along with Police Search and Rescue and LandSAR personnel and volunteers. 

Two helicopters have also searched from the air. 

- More to come