A man presumed drowned in floodwaters in Tasmania called his family from the roof of his van to say goodbye before being swept away on Tuesday morning.

Peter Watson, a 63-year-old contract delivery driver, and his partner Karen Cassidy were overcome by floodwaters while delivering Fairfax newspapers at Evandale, south of Launceston, about 3am.

After the couple accidentally entered an inundated road, they climbed onto the roof of their partially submerged van.

It was there Peter asked his son Corey Watson to deliver a message to his family.

"He was scared," Corey said.

"His biggest thing was to say how much he loved his family, his children Tanita Thynne, Natarsha Bett, Jessica Watson and Matthew Watson, and his stepchildren Claire Flice and Sean Cassidy.

"He said he'd watch over us always."

About an hour later, he was gone – swept away by floodwaters before a helicopter could rescue the pair.

Ms Cassidy was found clinging to a tree branch about five kilometres downstream hours later.

Peter is yet to be found and police hold grave concerns.

"It was a tough search," Tasmania Police Inspector Scott Flude said.

Emergency services will continue their search on Wednesday.

Ms Cassidy was treated for mild hypothermia and was kept under observation at the Launceston General Hospital for five hours.

She was released into her family's care in a stable condition, a hospital spokeswoman said.

A Fairfax Media spokesman said the company's thoughts were with Peter's family.

"Our heartfelt thoughts are with the family and colleagues of the contract delivery driver and his partner who were delivering newspapers for us when caught in floodwaters in Evandale near Launceston," a statement read.

"We're relieved the man's partner is safe – however our deep concerns remain for the driver who is still missing. All our support and care is being offered during this truly difficult time."

- The Examiner