Canberra was last night bracing for a second major storm as it cleaned up from Tuesday night's damaging "supercell" storm, which dropped up to 1m of hail and caused chaos in the centre of the capital.

Hailstones as large as golf balls and winds over 50kmh lashed the city for less than 30 minutes on Tuesday night but left trees defoliated and turned nature strips into mud baths.

The Bureau of Meteorology yesterday said the storm which hit Canberra was a supercell, the same type of storm responsible for the devastating twisters of tornado alley in the US.

"This storm was an ultra-efficient, thermo-dynamic machine," a bureau spokesman said.

"It feeds itself."

The supercell formed about 10pm on Tuesday and about an hour later it hit Civic, the centre of Canberra.

The storm forced the closure of the Australian National University, two high schools, government departments and many roads while it damaged the ACT Magistrates' Court and ACT Policing headquarters.

Canberra's main retail centre, The Canberra Centre, was forced to shut its doors as insurers moved in to assess the cost of extensive flooding in the recently redeveloped centre.

Bulldozers were called in early yesterday morning to clear metre-deep ice drifts in Civic as commuters awoke to peak hour horror in a city unused to traffic jams.