The Basslink undersea power cable connecting Tasmania and Victoria is down again, nine days after coming back online.

A statement from the company said it is believed the outage was due to a mechanical fault at the Loy Yang converter station.

The outage occurred at 6:18am and the company has advised the market it will be down until 6:00pm on Thursday.

Basslink said it was not unusual and it was not related to the outage in December that led to an unprecedented energy crisis in Tasmania.

"Such an outage is not an unusual occurrence across the electricity network," the statement said.

"Basslink is investigating the exact cause and hopes to have the issue rectified as soon as possible."

Hydro Tasmania was exporting power at the time the cable went down.

Government Minister Jacquie Petrusma described the outage as unfortunate.

"We need to keep in mind that our dams are nearly 28 per cent, heading fast for 30 per cent especially with the recent rainfall," she said.

"That outage is unfortunate, however we do have a robust energy supply plan in place to get us through these times."

Ms Petrusma would not say what advice Basslink had given the Government about the outage.

A team of about 100 cable experts spent almost six months fixing a tear in the cable before it was switched back on last week.

The cause of the original fault is still being investigated.

The lengthy outage combined with record low storage levels in Hydro Tasmania dams, putting pressure on power supplies and forcing the Government to import diesel generators.

An inquiry into Hydro's handling of the power crisis began on Monday.