Two people have been arrested after scaling the forecourt roof of Parliament House in Canberra to unfurl a banner protesting against logging in Tasmania's old-growth forests.

The man and woman were watched by a large crowd at the entrance to Parliament as they unfurled the banner, which read "Tasmania's ancient forests - world heritage, not wood chips".

The banner was attached to the coat of arms on the roof at the front of Parliament.

The protesters said they were aiming to send a clear message to the Rudd Government that logging of old-growth forests in Tasmania must end.

"Tasmania's ancient forests are not for sale, particularly for woodchips for the export market," the male protester said before abseiling back to the ground.

About a dozen police watched on as the protesters took 40 minutes to unfurl the banner before moving in to arrest the pair after they descended from the roof.

"Woodchipping is a plague on Tasmania's wilderness," the male protester said as he was led away by police.

A spokeswoman for the protesters, Lisa Stone, said the protest was part of a national day of action to highlight the damage being done to Tasmania's old-growth forests.

"We want the Government to call a halt to industrial logging of Tasmania's ancient forests," she said.

- AAP