More than a month's worth of rain brought the city to a standstill, as flash flooding damaged apartments and crept into underground garages across Canberra's north.

In the 48 hours from 10am Saturday, the Sullivans Creek weather station recorded 164.4mm, while Woolshed Creek had 95.4mm, the boat harbour on Lake Burley Griffin 74.8mm and Oaks Estate crossing 77mm. The Bureau of Meteorology said most of that rain fell within a couple of hours.

By Monday morning, the showers were easing but the clean up had just begun.

ACT emergency services responded to more than 250 calls overnight, and teams were back out again come 6am.

The Australian National University was forced to close on Monday after Sullivans Creek burst its banks, but a number of students living on campus remained on site to inspect the damage.

It is the first time the campus has been closed in 11 years.

The university told students all classes and events would be cancelled due to "significant flooding and power interruptions", as engineers assessed the safety of walkways and buildings, including Chifley Library.

Water rushed into the building's basement overnight, rising to about a metre and damaging a number of books in storage.

A university spokeswoman said the damage was still being assessed as safety checks continued.

One third year student on his way to the School of Music on Monday morning hadn't heard classes were cancelled.

"I've never seen something like this before here," he said.

A security officer watching over a closed off bridge on Sullivans Creek agreed it was the worst he'd seen in his time on campus.

Equipment had been swept into the creek from a nearby construction site at Union Court, which was itself four metres underwater during the storm.

While southbound traffic on Northbourne Avenue was down to one lane for much of the morning as the clean up continued, all lanes had reopened by 8.30am.

The Canberra Liberals have since requested an urgent briefing from the government, claiming damage from the storm could have been exacerbated by a "neglect of Canberra's essential stormwater assets".

An Auditor-General's report into the systems released late last month found many established areas had not been reassessed for flood risk mitigation, despite there being known risks in some areas.

Some of those areas were also unable to cope with major rain events, according to advice from Transport Canberra and City Services.

"[Infill] developments such as multi-unit high rise developments...reduce the amount of open space to help absorb stormwater so leading to more concentrated flows," the report said.

Shadow minister for urban services Nicole Lawder said her thoughts were with "all Canberrans who are cleaning up the mess caused in yesterday's flood".

"The event showed us the devastating effects of the government's inaction," Ms Lawder said.

"While not as flashy as light rail and shiny laptops, maintaining stormwater assets is a vital, taxpayer funded service."

As of 11.45am Monday, Oaks Estate Road had reopened, but Coppins Crossing remained closed along with Mount Franklin Road at Pidadilly Circus, Bendora Dam Road at Bulls Head and Googong southern gate at the London Bridge end.

All ACT government sports grounds are also closed until further notice and the Dickson pool has been flooded.

The Royal Canberra Show offered reduced fares on Sunday after cancelling some events throughout the day.

The Emergency Services Agency advised people to drive safely and "not enter any storm waters as rain may persist throughout the day".

According to the Bureau of Meteorology, those showers should ease by the afternoon ahead of a top of 20 degrees. Come Wednesday, the sun will be shining and the temperature soaring back up to 30.

For assistance during storms and flood call 132 500. For life-threatening emergencies call Emergency Triple Zero (000).

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