Thousands of people across Sydney have been ordered to leave their homes or remain on high alert as flooding worsens across the city.

The floods crisis also took another deadly turn on Tuesday, when the bodies of a woman and a man were found at Wentworthville, in Sydney’s western suburbs.

They are yet to be formally identified, but are believed to be 67-year-old Hemalathasolhyr Satchithanantham and her 34-year-old son Bramooth. They were reported missing on Monday after their car was found in a stormwater canal at Wentworthville.

New South Wales Police Detective Superintendent Paul Devaney said the water in the area rose “from ankle deep to about neck-high in a matter of minutes” on Monday.

“While we suspect that they are the occupants of the vehicle, the identities are yet to be confirmed through the formal identification process,” he said.

Eight people have now died in the floods that have hit NSW.

Elsewhere, NSW residents were urged to brace for a “tough 24 hours” as the rain showed little sign of easing. Up to 80,000 people are already subject to evacuation orders in NSW, with parts of Penrith and Lower Portland warned to be ready to evacuate on Tuesday afternoon.

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On the northern beaches, Manly Dam is spilling, spurring the likely evacuation of about 800 low-lying properties.

NSW SES Commissioner Carlene York said the dam was spilling but not at risk of failing.

The order is likely to affect residents along Manly Creek at North Manly and Manly Vale.

Dean Narramore, from the Bureau of Meteorology, urged people to follow orders issued by authorities.

“The rain is continuing across large parts of the metropolitan area, into the hunter and southwards into the Illawara,” he said.

“Since 9am, we have seen 50-100 millimetres in the northern suburbs and that is pushing up to the Central Coast,” he said in a Tuesday afternoon update.

“We have seen flash flooding in that part of the world and it is likely to move further north in the coming days and we have warnings for intense rainfall that is likely to lead to life-threatening and dangerous flash flooding.”

Earlier, Mr Narramore warned of “a tough 24 hours, or even 48 hours ahead” as the torrential rain kept falling.

• See all of the NSW SES evacuation orders and warnings here

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Sydney has endured 16 consecutive days of rain and no reprieve from the deluge is expected until Wednesday, with no sign of sun until Thursday.

A low-pressure system off the mid-north coast has brought torrential rain to the Hunter and greater Sydney regions and is moving towards the south coast. The intense rain is causing minor to major flooding from the Queensland border down to the Victorian border.

Ms York said the primary areas of concern were Kempsey, Georges River, the Hawkesbury Nepean River, Wollongong, Shoalhaven, St Georges Basin and Sussex Inlet.

“It’s very dangerous out there. There’s a lot of water on the roads and it’s prone to flash flooding as the heavy rains come,” she said.

The SES received more than 2500 calls for help in the past 24 hours and undertook around 200 flood rescues, mostly in Sydney.

The weather bureau has warned that saturated soil and swollen rivers could lead to landslides and flooding. Wind gusts of up to 90km/h are forecast, stretching south to the Illawarra region into Wednesday.

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Mr Narramore said widespread heavy rain overnight brought “devastating flash-flooding to some suburbs”.

“It was a dangerous night through parts of southern and south-western Sydney,” he said.

“Travel is definitely dangerous today not only because of rainfall … Tonight we’ll see possible trees and power lines down and landslips and flooding of roads.

“It’s still dangerous times out there.”

The Hawkesbury-Nepean was experiencing floods as bad as or worse than those in March last year, Mr Narramore said on Tuesday afternoon.

The severity will depend on how much more rain falls in the next 12 hours.

He advised residents stay inside and up to date with flood warnings and evacuation orders.

“But there is some good news, the low pressure system is moving off the coast,” Mr Narramore said.

Ms York warned residents to take evacuation orders seriously.

“There is no past history similar to this event. We’ve come out of the La Nina … the ground is saturated. The forecasts can never tell us exactly where the heavy rainfall is going to fall and the flow of the water has been quite dramatic,” she said.

“Listen to our orders and warnings, because your property may be affected even though it hasn’t been affected before.”

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Major flooding is occurring on the Macleay River, with parts of Kempsey in the north at risk of being inundated.

There is minor to moderate flooding in the Upper and Lower Hunter and major flooding on the Georges River in the Liverpool area.

The SES is warning river levels could rise along the Nepean and Hawkesbury rivers, potentially bringing “deep and dangerous flooding”.

Major flooding is occurring at Menangle, North Richmond, Wisemans Ferry and Putty Road.

Sydney Trains is asking commuters to avoid non-essential travel and allow extra travel time as it undertakes inspections to ensure the rail network remains safe amid the deluge.

-with AAP