A drink bottle believed to belong to a woman missing off the Catlins Coast has been found.

A search has continued today on foot, by boat and by plane for 77-year-old Whetuki Kopua and 60-year-old Matekino Burling.

Their overturned boat was found south of Nugget Point yesterday.

Police said the drink bottle thought to belong to Mrs Burling was found on the shore in between the two mouths of the Clutha River.

They said officers have also downloaded information from a GPS device from the vessel which gives an indication of where it may have capsized.

Both land and water searches will continue tomorrow.

The pair left Owaka yesterday morning on a fishing trip, but failed to return.

Around 60 searchers scoured the South Otago coastline yesterday, with a helicopter, planes and boats also used.

The boat they were in is a 5.2 metre pontoon style Kiwikraft boat.