A third person has died after an horrific crash involving a Cancer Council minibus in northern Tasmania.

A man and a woman died earlier at the scene of the accident in Elizabeth Town west of Launceston.

The third person died during surgery, police said.

The bus was carrying 10 elderly passengers, believed to be on their way home to Burnie after receiving cancer treatment when it and a trailer that came loose from another vehicle collided.

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The bus then hit a power pole, leaving a mangled wreck.

The other passengers were taken to two hospitals, several with serious injuries.

Tasmanian Cancer Council chief executive Simon Barnsley said the organisation was in shock at the accident.

"Our staff and volunteers are distressed and saddened by the news and we extend our sympathies to the families of those affected," he told the ABC.

Mr Barnsley said counselling would be offered to those affected.

Acting premier Bryan Green was among the first to express his sympathy.

"I realise that at times like this words can mean very little, but I wish everyone coping with the aftermath of this crash every strength for the time ahead," Mr Green said.

Opposition spokesman Jeremy Rockliff added his concern.

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"My heart goes out to the families and friends of those affected by this terrible tragedy," he said.

The Bass Highway was expected to be closed for several hours.

- AAP