Drivers are being warned to avoid non-essential travel as the dangerous storm system hits along Australia’s eastern seaboard.

An inland low and coastal trough joining forces over NSW is forecast to bring significant falls.

“We’re expecting the interaction between these systems to really increase the rainfall over eastern NSW,” Bureau of Meteorology meteorologist Helen Reid said on Friday.

“We’re going to see widespread rainfall with heavy to locally intense rainfall expected,” she said.

Authorities warned 24-hour totals could top 200mm in Sydney and the south coast, with as much as 300mm dumped on the Illawarra Escarpment overlooking Wollongong.

More than 107mm has fallen in the Sydney’s city centre at since 9am on Thursday.

The ongoing intense downpours could lead to “dangerous and life-threatening flash flooding” from Friday evening, NSW’s State Emergency Service warned.

The State Emergency Service is urging residents of Sydney, Gosford, Wollongong, Nowra, Batemans Bay and Goulburn to “stay indoors” due to the dangerous weather.

The agency responded to 552 incidents in the 24 hours to 5am on Friday, including seven flood rescues.

“Six of those related to people in vehicles, so we are asking people not to travel if they don’t need to,” NSW SES chief superintendent Dallas Burnes told the ABC.

Dangerous winds could topple trees out of the soaked ground and SES crews were being moved into position.

“We’re keeping a very close eye on where those falls are landing to make sure that we’ve got teams ready to respond,” Supt Burnes said.

Major flooding was possible along the Hawkesbury Nepean River bounding Sydney from late Friday, with Penrith likely to cop as much rain in a day as one-and-a-half Aprils.

Transport NSW took the rare step of warning drivers statewide to avoid non-essential travel.

“For those who need to travel, please take your time and plan ahead by checking Live Traffic NSW to see if your route is impacted by severe weather,” a spokeswoman said.

The storm has already claimed a life in Queensland after the body of a man was found by his ute near Logan, while a 30-minute wave of rain in northern NSW flooded enclosures at a wildlife sanctuary on Thursday.

“Due to the amount of water dumped into the park, we have relocated our animals and the hospital (has been) re-located to a higher position,” Byron Bay Wildlife Sanctuary said.

With the catastrophic 2022 Northern Rivers floods fresh in minds, the SES said the silver lining for Friday’s system was that it was moving.

“If we go back to those northern river floods, it didn’t move as forecast,” NSW SES Commissioner Carlene York said.

“It stayed there, it kept dumping the rain and that’s obviously had the big impact.”

Her legion of volunteers have proactively deployed vehicles and vessels into danger areas.

Residents in such areas should clear gutters and tie down loose items ahead of time, Metro Zone Commander Allison Flaxman said.

She urged them to download the official Hazards Near Me app to stay abreast of latest warnings.

The weather bureau said catchments were fairly wet in the north and average to dry around Sydney and the south coast.

But the prospect of water releases down the Hawkesbury Neapan River mean Australia’s largest urban water supply dam threatens to spill.

Warragamba Dam, on Sydney’s southwestern fringe, sat at 96 per cent capacity as Friday’s storm approached.