There is not a lot left in the small Tasmanian farming town of Tunbridge, with only about 90 people remaining to call it home.

Key points: The 1848 convict-built bridge over Blackman River in Tunbridge is believed to be the oldest surviving wooden-decked bridge in Australia

The 1848 convict-built bridge over Blackman River in Tunbridge is believed to be the oldest surviving wooden-decked bridge in Australia The bridge was damaged in a deliberately lit fire on Christmas Eve last year, but with three government departments involved in its upkeep, a decision on how to repair it has yet to be made

The bridge was damaged in a deliberately lit fire on Christmas Eve last year, but with three government departments involved in its upkeep, a decision on how to repair it has yet to be made With traffic diverted from the bridge until it is repaired, locals just want it fixed

The Midlands Highway bypasses it now, the shop has shut and so has the pub.

Now, the town's remaining claim to fame and tourist lure — Australia's oldest single-span wooden bridge — is under threat.

The 1848 convict-built bridge, over the Blackman River, is also believed to be the oldest surviving wooden-decked bridge in Australia, and part of the tourist Convict Trail.

A deliberately lit fire last Christmas Eve severely damaged the wooden spans and decking.

Southern Midlands Mayor Alex Green said the bridge had been shut to traffic since and it could be years before it reopens.

"The bridge has been [in a] deteriorating condition for a number of years and then on Christmas Eve there was a fire … which has really brought forward the issue of a replacement," he said.

The bridge has been closed since it was damaged by fire. ( ABC News: Edith Bevin )

Rodney Hazelwood, 76, said even without the fire, the bridge's days had been numbered.

"It was just rotted away … it was only going to be a matter of time before it was closed up completely," he said.

As well as being a historic structure, the bridge was also the northern exit out of the town, enabling access to the farms surrounding the township.

Locals said they just wanted their bridge reopened.

"We've got to have it really, what if something happens at the other end of the town? How do we get out if there's no bridge down here," Mr Hazelwood said.

Fears bridge fix could cost town character

But it is how to repair the bridge that has the town residents divided.

Three options have been put forward — replace the damaged wooden spans with new timber, concrete the bridge, or replace the timber spans with more durable engineered beams and concreting the top.

"I reckon the third option [concrete and sandstone]," Mr Hazelwood said. "The one that will last 100 years."

"Not that I'll be here in 100 years, none of us will be, but at least there will always be a bridge here," he said.

The bridge pictured in 1955. ( State Library of Tasmania )

That option would also see the bridge re-opened to heavy farm trucks and machinery. Before the fire there was a five-tonne weight limit.

But others, like resident Kevin Sanford, said they were worried if the bridge was concreted it would cost the town its character and tourism drawcard.

"Anyone who coming in to this town, sees this sign that says 'welcome to Tunbridge' and a beautiful photo of the old wooden bridge," he said.

"So, if they are going to bastardise the old wooden bridge, you need to take the signs down, because they're irrelevant and Australia's oldest wooden bridge will be a thing of the past."

Three agencies in control

The bridge has historically been the marker for Tasmania's parochial north-south divide.

That divide is further complicating its repair — while the town of Tunbridge comes under the Southern Midlands Council area, the bridge is an asset of the Northern Midlands Council.

And as a public road, it is also the responsibility of the Department of State Growth.

"There are basically three Government bodies with an interest in this bridge," the Cr Green said.

"The Blackman River has been seen as a boundary between north and south and here we have a beautiful example of how that is."

Some locals fear concreting the bridge will detract from the town's character. ( ABC News: Edith Bevin )

Mr Sanford said the north-south divide was part of the reason the bridge has deteriorated so badly.

"It hasn't been well-maintained, I'm one of the people that's rung up and said 'there's great spikes sticking up in the bridge again' and it seems to be an argy-bargy story about oh well its with the Southern Midlands and it's not our problem, it's with the Northern Midlands and you don't know who owns what," he said.

The historical marker of division might be the thing that unites the longtime rivals.

Cr Green said a joint planning authority may need to be investigated "where both councils act together as a planning authority in order to see a replacement built".

"We are we certainly firmly committed to seeing the right decision on the right side of the Blackman River."

The Northern Midlands Council was contacted for comment.