Torrential rain has hit the Hunter Region, raising the risk of "life-threatening flash flooding", the Bureau of Meteorology said.
The bureau issued a severe weather warning for the Hunter on Sunday morning, asserting that flash flooding was expected.
"There is potential for periods of very heavy rainfall and life-threatening flash-flooding in the Hunter, including the Central Coast," the bureau said.
"Abnormally high tides are expected this morning, around which time the sea water level may exceed the highest tide of the year."
The bureau further forecast dangerous conditions including very heavy rain and high winds, along with large waves and tides.
Nelson Bay had received 102 millimetres of rain and University of Newcastle 75 millimetres of rain in the 24 hours to 9am on Sunday, the bureau said. Lake Macquarie had received 84 millimetres, Williamtown 66 millimetres, Maitland Airport 66 millimetres, Nobbys Head 50 millimetres, Scone 32 millimetres and Murrurundi 29 millimetres over that same period.
Areas around Lake Macquarie were experiencing minor flooding on Sunday morning, particularly around the shore and low-lying areas such as the Belmont-Swansea area.
Water levels were running high in Swansea Channel. Dive Newcastle posted a video of water rushing furiously under Swansea Bridge.
Surf and swell conditions were expected to be hazardous for coastal activities such as rock fishing, boating, and swimming in the following areas.
At 12.30pm on Sunday, train services were suspended between Gosford and Morisset in both directions due to external power supply issues affecting signalling and track equipment at Wyong.
Bus companies were being contacted to run a replacement service.
Power was out in Cams Wharf, Catherine Hill Bay, Caves Beach and surrounding suburbs from about 9.30am. Charlestown, Kotara, New Lambton and surrounding suburbs also lost power, before it was restored at about 11.30am.
The bureau said moderate flooding may occur along the Gloucester River at Gloucester on Sunday morning.
The State Emergency Service had been busy responding to about 185 call-outs in the Lower Hunter from midnight on Saturday to Sunday morning.
The SES issued a minor flood warning for Tuggerah Lakes on the Central Coast on Sunday morning.
"Heavy rainfall has been observed in the past 24 hours over the Tuggerah Lake catchment," an SES statement said.
"Further heavy rainfall is forecast for the next 24 to 36 hours which may cause further river level rises. A severe weather warning is current and potential for very heavy rainfall in the Central Coast and Hunter, particularly during Sunday."
The SES urged people to closely monitor the situation and plan ahead around possible road closures and inundation of low-lying areas if lake levels continue to rise.
It warned people to: avoid drowning; stay out of rising water; seek refuge in the highest available place; prevent damage to your vehicle; move vehicles under cover away from areas likely to flood; avoid being swept away; stay out of fast-flowing creeks and storm drains; never drive, ride or walk through flood water because flood water can be deceptive and dangerous.
Lake Macquarie City Council cancelled the Morisset Show due to the weather, while a 20th anniversary celebration for Central Coast Stadium was postponed.