Basslink is planning a major operation to repair its undersea power cable which has been shut down, halting power imports to Tasmania.

Tasmania is relying on power produced within the state after a fault was detected in the cable on Sunday afternoon about 100 kilometres off the Tasmanian coast.

The cause is of the fault is being investigated.

Hydro Tasmania had been importing about 40 per cent of the state's electricity needs from Victoria due to low water storages.

Energy Minister Matthew Groom said the Government had instructed Hydro to suspend the proposed sale of the Tamar Valley Power Station as a result.

He said the Government was reviewing "the very unusual circumstances" that Tasmania was experiencing with low water storage levels in dams combined with the Basslink issue.

Hydro Tasmania informed the Minister this morning that it was in a position to meet electricity demand for the 60 days Basslink has to fix the fault.

"It's important not to assume though that that would be an estimate of the outage," Mr Groom said.

"Hydro Tasmania are in a position to be able to supply all supply requirements at present."

The Basslink cable connects Tasmania with Victoria and allows for the import and export of electricity.

Power will be supplied through Hydro Tasmania's water storages, wind facilities and the Tamar Valley Power Station.

'Marine disaster plan' enacted

Basslink CEO Malcolm Eccles said a team of experts had been assembled to diagnosis and repair the fault.

"Until we actually get eyes on the cable we really have no idea what the cause of the problem is," Mr Eccles said.

"We're confident our marine disaster recovery plan is correct, we also believe we've got the right skills so we're quite confident of this repair process."

A ship is being brought from New Zealand and will be kitted out in Melbourne before heading into Bass Strait to repair the fault.

Hydro Tasmania spokesman Ian Colvin said it was informed on Sunday about a fault but that it was not made aware of the seriousness of it until today, when Basslink issued a press release and informed the markets.

He said the cable had "tripped" on other occasions.

Opposition Leader Bryan Green has questioned why the Government did not inform Tasmanians about the shut down earlier.

"When did Mr Groom find out about this potentially very ominous situation that could take a very long time to repair?" he said.

"Yesterday he was happy to swan about trumpeting his Three Capes announcement and didn't tell Tasmanians he was sitting on a potential energy crisis.

"The indefinite outage will put enormous pressure on Tasmania's energy supply, with water storage at unusually low levels for this time of year."

It is not the first time the cable has suffered an outage. In August 2006, the cable went down for two-and-a-half hours.

The gas-fired Tamar Valley Power Station is being brought back on line because of low Hydro dam levels.

It is expected to be operating by January 18.