A severe weather warning is in place for all eastern NSW and the ACT, as the bureau warns of heavy rainfall, damaging winds, damaging surf and abnormally high tides.

While conditions are not expected to be as severe as north of Sydney, Canberrans are being warned to brace for further heavy rain and potential flooding on Tuesday, when up to 90 millimetres is forecast to hit the region.

There have already been two significant traffic accidents in the wet weather, and the downpour has been keeping State Emergency Services crews busy to call outs across the city. The SES received 85 calls for help between midnight and noon, when 45 were still outstanding.

"The requests for assistance have consisted of leaking roofs, fallen trees, powerlines down and flooded roads across Canberra," it said.

"For assistance in a storm or flood call the ACTSES on 132 500, in a life-threatening emergency call Triple Zero (000)."

Queanbeyan's State Emergency Service volunteers spent much of Monday night preparing to hit the ground running ahead of the deluge.

Some minor flooding has already been recorded in Queanbeyan as of Tuesday morning, with the Morisset Street bridge closed due to the rising waters, along with the Oaks Estate Crossing. Naas bridge in Namadgi National Park collapsed in the early hours of Tuesday.

And the Murray-Darling Basin Authority posted video of Googong Dam spilling into the Queanbeyan River, which flows into Molonglo River and then into the Murrumbidgee River.

The Bureau of Meteorology has forecast between 50 and 90 millimetres to fall in Canberra and surrounds, as a severe weather warning was issued on Monday.

The warning is for damaging winds, heavy rainfall, abnormally high tides and damaging surf, and encompasses most of NSW.

In the 24 hours since 9am on Monday, Tuggeranong recorded 51 millimetres while Canberra Airport got more than 30 millimetres. Another 13mm had fallen at the airport in the three hours to noon Tuesday.

It comes as NSW Premier Gladys Berejiklian said on Tuesday morning that overnight weather conditions had worsened in flood-affected areas across the state.

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Forecaster at the bureau Helen Reid said while large-scale flooding seen in north-western Sydney and across the mid-north coast of NSW was not expected in Canberra, heavy rain was predicted, driven by the same weather system engulfing NSW.

"Canberra is more likely to reach the 50-70 millimetre mark on Tuesday, but people will notice it more as consistent rainfall for many hours of the day, but not flooding," she said.

"We are expecting some river flooding around Queanbeyan throughout the day and all river catchments will be full."

Multiple low-lying roads have been closed off around the region, including the Morisset Street Bridge in Queanbeyan, Oaks Estate Crossing, Coppins Crossing, Point Hut Crossing and Uriarra Crossing.

Many of the road closures in Canberra were driven by the opening of Scrivener Dam about 9.30pm on Monday.

According to Icon Water, ACT and Queanbeyan dams are completely full for just the second time since the enlarged Cotter Dam was completed in 2013.

Corin and Cotter dams were at capacity on Monday morning, and by the afternoon so, too, were Bendora and Googong dams. Combined, they hold 277.83GL.

They had dropped to below 45 per cent - or 123.6GL - in February last year.

SES crews have responded to dozens of calls for help in the region, with additional crews on standby on Tuesday ahead of the heavier falls forecast for Tuesday.

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The bureau has also warned of very heavy surf south of Moruya, and the risk of localised damage and coastal erosion. Abnormally high tides could also cause sea water flooding on Tuesday morning.

The bureau has also issued a "minor flood watch" for Queanbeyan for Tuesday.

Eight flood evacuation orders have been issued for the NSW mid-north coast as wild weather and torrential rain continues to lash much of the state's east.

Heavy rain is likely to lead to flash flooding and will remain a serious risk for the Northern Rivers and Mid-North Coast on Monday and Tuesday, the bureau warned.

Risks remain for the Hunter and Central Tablelands districts, particularly as catchments are already saturated.

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Drier conditions are predicted from midweek. Wednesday is expected to be cloudy with a potential shower with a top of 22 degrees.

Sunnier conditions are forecast for Thursday and Friday; both days are expected to be partly cloudy.

There is a slight chance of rain on Thursday, which is forecast to reach a slightly warmer 23 degrees.

The weekend will likely begin with a grey start. Saturday is predicted to be cloudy while Sunday expected to be partly cloudy, with maximum temperatures for both days forecast to reach 22 degrees.

The State Emergency Service advises that people should:

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