Hydro Tasmania says the Bassslink power cable is protecting the state from power rationing in the lead-up to winter.

The Bell Bay power station is expected to remain shut until at least tomorrow, and possibly next week, because unexpected urgent maintenance work at a Victorian gas supplier has left the station without any gas.

Hydro will use one-fortieth of its remaining water storages to keep the state running for two days, and is also buying power from interstate.

The company's Andrew Catchpole said water storages were down to 20 per cent of capacity and would be down to about 14 per cent if Basslink was not topping up electricity supplies.

Mr Catchpole said the state could certainly generate below that level and the issue becomes meeting the peaks in demand that occur on cold winter mornings.

He said that's when there could be some form of rationing - perhaps up to 100 megawatts.