Fast-moving thunderstorms have brought heavy rain with golf-ball-sized hail stones lashing the ACT and there could be more to come.
Widespread damage from the first wave of storms has been reported across Canberra, but appears to be particularly concentrated in the Belconnen suburbs, city and inner south.
The Emergency Services Agency has received more than 600 calls for help, and is warning people that the high volume of calls means there might be delay getting through. If you need help, call 132 500 and only use Triple Zero (000) for life-threatening emergencies.
"We ask for your patience at this time and your call will be answered as quickly as possible," it said.
"The ACT State Emergency Service, ACT Fire & Rescue and ACT Rural Fire Service are working together to respond to hail and roof damage, electrical threats and localised flooding."
There are reports of smashed car windscreens, flooding, broken windows, dented vehicles, trees down and branches shredded. There are dozens of reports of power down, especially in Belconnen and inner south.
Police are reminding drivers it is illegal to drive a car with a cracked or shattered windscreen.
A tree has fallen on Northbourne Avenue, affecting traffic.
Video posted online also showed a roof leaking at Westfield Belconnen, and the hailstones were described as being "like bullets" as they punctured the roof of the National Film and Sound Archive. Belconnen Basketball stadium is reporting damage to the indoor courts.
The ANU has issued a "shelter in place hail event" alert, telling staff and students to "shelter in place if it safe to do so ... There may be more more storm fronts on the way so travelling at this stage is not advised".
As of 1.50pm, ACT emergency services have received 620 requests for assistance since noon. They have responded to reports of hail and roof damage, electrical threats and localised flooding.ACT Ambulance Services have treated two people for minor injuries sustained during the storm.
The Bureau of Meteorology has warned there could be more to come.
"There is a possibility we get some more ... that might be just the first wave," Bureau forecaster Abrar Shabren said.
Mr Shabren said storm activity was recorded across the whole of the ACT but that parts in the north have been hardest hit.
The Bureau of Meteorology issued a severe warning on Monday morning as heavy storms formed west of Canberra with a northwesterly forecast to push the system into the city.
Earlier, Mr Shabren said the system was fast-moving and winds could bring the most damage. He warned of golf-ball-sized hail stones.
"Damaging winds are the most likely phenomena with fast-moving thunderstorms," he said.
"Short sharp bursts of rainfall are expected."
Emergency Services Agency ACT commissioner Georgeina Whelan said the ACT was in for an "intense couple of hours" and storm activity was expected to hit most parts of the territory.
"We normally see some storm activity to the north or the south of the ACT, not necessarily the entire region [but] today we could actually see from the north of Canberra right through to the southern tip of our borders actually being impacted by storms, winds and lightning strikes," she said.
Chief Minister Andrew Barr said the ACT State Emergency Services had been stood up to respond to the impending storm.
People have been advised to move their cars under cover or away from trees, secure loose items around the house, yard and balcony, keep clear of creeks and storm drains and not to walk, ride or drive through flood water.