More than 30,000 people are under evacuation orders as communities in Sydney’s west, north-west and south-west brace for more deluges and a worsening flood crisis on Monday.

With some communities inundated for the fourth time this year, there were 71 evacuation orders and 64 warnings in place, covering about 32,000 people.

There is most concern for the Hawkesbury-Nepean area north-west of Sydney, where the flooding is worst.

Some areas have already had hundreds of millimetres of rain, with more heavy falls expected on Monday, the weather bureau’s Jane Golding said.

“It is dangerous out on the rivers and we do have some more rain
to fall, which means the flash flood risk is not over yet either,” she said.

“We are still seeing a steady stream of showers … we’re expecting rainfall for some locations to be very high again today,” she said.

Tweet from @BOM_NSW

The flood risk will remain even after the rain stops, with saturated catchments likely to react quickly to any rain in the next couple of weeks.

The federal government has committed more defence force support following a second request from the NSW government, sending two ADF night-time helicopters and 200 troops to assist during the crisis.

Emergency Management Minister Murray Watt warned the latest flood event could be the worst in the past 18 months.

“The latest information we have is that there’s a very good chance that the flooding will be worse than any of the other three floods that those areas had in the last 18 months,” he said.

Prime Minister Anthony Albanese, who has been in Ukraine, confirmed via Twitter on Monday he had had briefings from Senator Watt and NSW Premier Dominic Perrottet.

Tweet from @AlboMP

Mr Perrottet said the federal response so far had been “incredibly pleasing” and the immediate deployment of the ADF was an improvement on earlier floods.

“It has been a very difficult time for many months [and then] to have this flood event off the back of others. It makes it more challenging and once again, our SES are on the frontline day in, day out,” he said.

“If there is an evacuation warning in place, please get ready to evacuate. If there is an evacuation order in place, please leave immediately.”

There are also concerns for a bulk carrier that lost power off the NSW coast, after leaving Wollongong on Monday morning. The Portland Bay has 21 crew on board, and was only about a kilometre off the coast.

“It is obviously a very precarious position and our thoughts are with those on board,” Mr Perrottet said.

The vessel has since been anchored and tugboats have arrived to assist. Plans to airlift the crew from the ship earlier were delayed by the rough weather.

Areas stretching from Newcastle to the south coast and as far inland as Oberon are at risk from this week’s weather, but especially western Sydney’s flood-prone Hawkesbury-Nepean area.

The wet weather system that has wrought havoc across parts of Sydney is expected to move south along the Hunter, central and Sydney coasts in the next 24 hours.

The bureau has issued flood warnings for the Hawkesbury, Nepean and Colo rivers, where levels in some parts of these catchments have already exceeded levels recorded earlier this year.

The bureau warned river levels could reach those of March, when swathes of Sydney’s south-west and outer west were inundated.

The SES responded to more than 400 requests for help overnight and performed about 20 flood rescues. Those numbers are expected to increase.

Among those rescued were a mother and her six-week-old baby from Gronos Point, on the northern banks of the Hawkesbury River.

Camden Council deputy mayor Paul Farrow said the south-west Sydney community was heartbroken and fatigued by repeated flooding over the past 18 months.

“It’s the worst case of deja vu you could possibly imagine,” he told Sky News on Monday.

“We’re becoming used to it unfortunately.”

Risk Frontiers resilience general manager Andrew Gissing said community flood recovery could be hindered by repeat events.

“They are forced to continually pick up the pieces,” he said.

Mitigation strategies and encouraging development in lower risk areas could reduce flooding in the future, he said.

Warragamba Dam began spilling on Sunday morning, and by night water was gushing over the wall at a rate of 515 gigalitres a day.

WaterNSW said the flow slowed overnight, down to 380GL/day, but the spill would depend on Monday’s rain in the catchment. The dam flows into the swollen Hawkesbury and Nepean rivers, which are above major flood levels in multiple areas.

Evacuation centres are open in western Sydney at Canley Vale’s Cabra-Vale Diggers Club, the Narellan community centre, Gymea Tradies Club, Richmond Club, North Richmond community centre and Castle Hill RSL.

Ms Cooke said 184 people had registered at evacuation centres and 68 people were in emergency accommodation.

Evacuation orders in place in parts of:

• Wilberforce, Londonderry, Wisemans Ferry, Ebenezer, Riverstone, Pitt Town, Pitt Town Bottoms, Agnes Banks, South Maroota, Lower Portland, Yarramundi, Penrith, Wallacia, Emu Heights, Emu Plains, Sackville, Leets Vale, Cumberland Reach, Oakville, Windsor, North Richmond, Freemans Reach, Agnes Banks, Bligh Park, Richmond Lowlands, Angus, Cattai, Cornwallis, Gronos Point, Plough and Harrow Dam near Abbotsbury and Cecil Hills, Pleasure Point, Bents Basin, Camden, Woronora, Chipping Norton, Georges Hall, Lansvale, Moorebank, Warwick Farm

Evacuation warnings are in place in parts of:

• Shanes Park, Schofields, Vineyard, Windsor Downs, Marsden Park, Melonba, Mulgoa, Clarendon, Leonay, McGraths Hill, Mulgrave, Lake Illawarra, Cranebrook, Regentville, Castlereagh, East Hills, Picnic Point, Elderslie
• See all the latest evacuation orders and warnings at NSW SES

Major flooding occurring along:

• Hawkesbury River at North Richmond (14.1 metres, rising) at Windsor (12.71 metres, rising) and at Lower Portland (7.61 metres, steady), Nepean River at Menangle Bridge (13.52 metres, rising)

Moderate flooding occurring along:

• Nepean River at Camden Weir (10.53 metres, steady) and at Penrith (8.43 metres, rising), Hawkesbury River at Sackville (7.69 metres, rising)

-with AAP