Ferry services in the Cook Strait are cancelling crossings due to heavy swells on Tuesday.

A strong southerly wind is bringing large swells and gusts.

Interislander services between Picton and Wellington at 9.30am, 3.30pm and 9.30pm were cancelled on Tuesday, as well as the 3.30am on Wednesday 19 August.

"Safety is our priority and we only sail when it is safe to do so," said Interislander.

It said passengers would be contacted and rebooked to a different service.

Bluebridge has cancelled sailings between Wellington and Picton at 1.30pm.

"Due to limited re-booking options, standby lists across subsequent sailings will be operating from each port for affected customers to be added to," Bluebridge said.