Police are evacuating 21 houses along the Hawke's Bay coastline.

The houses at Haumoana have been under threat since the weekend from high swells and rough seas. People along the wider coastline including Waipatiki, Whirinaki, Te Awanga, Clifton, Ocean Beach and Waimarama are being asked to evacuate.

Senior Sergeant Ross Smith says big swells are threatening the area.

"We're expecting swells of between 3.5 and 5.5 metres along Haumoana, Te Awanga and Clifton beaches. And up to (6.5 metres) in Ocean Beach and Waimarama Beach.

People are being asked to stay away from beaches and low-lying areas.