More than 18mm of rain has fallen since 9am on Saturday, with a total of 53mm since the dreary weather began on Friday evening.

ACT Policing attended three car collisions in the morning and warned traffic lights were failing across the city, including the intersection of Gungahlin Drive and Belconnen Drive and the intersection of Gungahlin Drive and Belconnen Drive.

Police told Canberrans to only cross intersections with flashing yellow lights when safe and to give way to the right. Ecowise was responding to the traffic light malfunctions.

The ACT State Emergency Service (ACTSES) has received 179 calls for assistance since 5pm on Friday, mostly relating to backyard and garage flooding as well as leaking roofs. No injuries or serious damage has been reported.

The ACTSES has advised people not to climb onto roofs to remove leaf litter in the wet conditions.

Motorists across Canberra have been slowed by localised flooding, as the heavy downpours cause pooling across some roads and intersections.

Angle Crossing is closed due to the wet weather, as is the McCulloch Street Underpass in Curtin.

Warnings from the Bureau of Meteorology said a tropical, warm and humid airmass over New South Wales would interact with a complex low pressure system moving through Saturday.

A severe weather warning is in place for heavy rain which may lead to flash flooding in the ACT. Including rainfall already received, 48-hour totals are likely to exceed 100mm with localised falls in excess of 200mm in some parts of NSW.

Locations which may be affected include Canberra, Cooma and Yass, while the warning also extends to Condoblin, Wagga Wagga, Albury, Young, West Wyalong, Tumbarumba, Deniliquin, Griffith and Narrandera.

A flood watch is in place for Southern and Central Western NSW.

Damaging winds averaging 80 to 90km/h with peak gusts in excess of 110km/h are possible over the Alpine peaks above 1900 metres.

Director of Roads ACT Ken Marshall reminded road users to exercise caution when travelling.

"If a high level of rainfall occurs, it is possible a number of rural roads could be affected, along with some unsealed reserve and forestry roads, such as fire trails," Mr Marshall said.

"For your own safety, please obey all directions from traffic management staff and signage.

"Motorists should drive to conditions. Do not attempt to cross a flooded road, bridge or causeway and if driving becomes too difficult pull over safely to the side of the road and wait until conditions improve."

Prime Minister Malcolm Turnbull was among political leaders reminding Australians not to drive, ride or walk through flood water.

On Thursday, forecasters warned heavy rains will lash the capital this weekend, as a significant storm system sweeps across Australia's south-east.

The conditions has meant a number of events have been cancelled on the weekend, but the Christmas in the city celebrations are going ahead.

Residents are advised to move vehicles under cover or away from trees, secure or put away loose items around their house, yard and balcony and to keep at least eight metres away from fallen power lines or objects that may be energised, such as fences.

If you find distressed wildlife, report it to 13 22 81.