Bushfires raging across Tasmania have forced residents to flee their homes, burned a homestead and closed parks over the Australia Day long weekend.

Fifty-six blazes were burning in the state on Saturday, with 28 of them uncontrolled amid tinder-dry conditions.

Weeks of dry and hot weather summer has wreaked havoc across south-eastern Australia, although cooler temperatures on Saturday brought some relief to Tasmania, along with Victoria and South Australia.

In New South Wales, water minister Don Harwin said Sydney’s desalination plant would be activated on Sunday with dam levels expected to fall below the threshold figure of 60%.

Tasmania’s central plateau fire had doubled in size, said Tasmania fire service state public information officer, Peter Middleton.

“There is still a lot of fire, it is very dry, we want people to be vigilant and not venture into the fire areas,” Middleton said.

An uncontrolled bushfire at Riveaux Road and Tahune Airwalk was putting Castle Forbes Bay, Geeveston, Port Huon, Cairns Bay and Waterloo at risk on Saturday afternoon with embers and ash threatening property.

Middleton said it was difficult to determine how many people had been displaced but 230 people were in the main Huon Valley evacuation centre on Friday night and 200 had slept there.

Three structures were reported destroyed – a homestead, a kayak shed and a fishing shed – as the fires razed 87,000 hectares.

A fire that will be come uncontrollable at Lake Echo and surrounds is putting those communities at risk while another fire on the central plateau was also threatening Jean Banks Road, Waddamana.

Fire services were devoting every available resource at the 9,800km of fire lines with 32 aircraft and 540 firefighters battling the blazes, 140 of them from interstate and New Zealand.

Bushfires approaching Waddamana, Hilltop and Penstock Lagoon were putting those communities at very high risk and an emergency warning was also in place for the Bashan area at 2pm on Saturday.

Some national parks and reserves remain closed due to the fire risk, including the Tasman National Park, Freycinet National Park and Cradle Mountain-Lake St Clair National Park.

People were being told to stay away from the bush for the whole long weekend, with a total fire ban in place across the state until 2am on Monday.

At least one of the fires has been burning since late December.