The ACT State Emergency Service has received 491 calls for help and 236 jobs remain outstanding.

Power is still out in Evatt, Florey, Flynn, Hawker, Kaleen, Latham, Macgregor, Melba, Spence and Weetangera.

The thunderstorm dumped almost 40mm on the city over three hours and caused the Australia Day fireworks to be cancelled and Calvary Hospital to lose all power for about a half hour.

And the latest forecast from the Bureau of Meteorology says there is the chance of another storm tonight and a 90 per cent chance of more rain.

Meanwhile, a sixth tornado has hit Queensland's Bundaberg region and forecasters say more could develop, including over Brisbane, as the day wears on.

In Canberra, fresh crews from emergency services, ACT Fire & Rescue, Rural Fire Service and Territory and Municipal Services have been responding to call outs from early Sunday morning. Most are for leaking roofs, flooding and fallen trees and branches. As of noon, there were 236 jobs outstanding.

They are expecting even more calls today and tomorrow as people return home from trips away over the long weekend. For help, call the SES on 132 500.

Authorities are asking people to be patient, saying they are working through jobs as quickly as possible.

"Calls have been prioritised based on the level of damage and risk to the community," the ESA said in a statement.

ActewAGL staff worked overnight to restore power to about 3500 customers who lost their power. About 10am, ActewAGL said crews were still working in Evatt, Florey, Flynn, Hawker, Kaleen, Latham, Macgregor, Melba, Spence and Weetangera. Updates on power outages are available on the ActewAGL website.

The city's northern suburbs appeared to have copped the brunt of the storms.

Large limbs are still strewn across front yards and nature strips, while basements in apartment blocks have become shallow pools of stormwater.

A public housing tenant in Belconnen called The Canberra Times to say their roof had caved in under the weight of water.

ACT Policing says severe storms caused the Australia Day fireworks to be cancelled and havoc elsewhere across the territory.

Falling trees blocked roads and caused several traffic lights to black out, requiring traffic management and flash floods were reported. Oaks Estate low-level crossing has now been reopened.

The Bureau of Meteorology forecasts scattered showers and the chance of thunderstorms today, with light winds becoming north easterly, up to 20 km/h later on Sunday evening. There is a 90 per cent chance of rain.

The thunderstorms on Saturday night caused Calvary Hospital to lose all power.

The hospital lost power, both main and auxiliary, for about 30 minutes during the storm.

No patients were affected and no surgery was being conducted during the storm.But the hospital came close to declaring a ''code yellow'', or an internal disaster, after the auxiliary power failed to kick in automatically.

A hospital spokesman said the issue was being rectified, and was caused by the abnormal and incredible volume of rain.

The thunderstorms dumped huge amounts of rain over the ACT, first hitting the north and western areas, before moving south through Woden and Tuggeranong.

More than 38 millimetres of rain fell at Canberra Airport between 6.39pm and 9pm, while strong winds gusted up to a maximum of 54km/h during the evening.

A reported 70 millimetres of rain fell at Murrumbateman, to the ACT's north.

The Fireworks Spectacular at Lake Burley Griffin, billed as an impressive finale to Canberra's Australia Day celebrations, was cancelled just before 8pm, an hour before the display was scheduled to start.

Organisers said they were forced to cancel the event for public safety reasons, and many of those gathered at vantage points around the lake were forced to flee to shelter earlier in the evening.

The State Emergency Service had responded to 120 calls for help by 7.59pm, many of which related to flooding and fallen trees.

There were no reports of major damage, but extra ACT Fire and Rescue crews and Queanbeyan firefighting crews were activated to cover the busy period.

More than 80 automatic fire alarms were set off during the storm, forcing responses from fire crews.

Emergency services were also urging Canberrans to stay out of the floods, and away from stormwater drains after the storm passed.

with John Thistleton