NSW has been told to prepare for a “difficult week” and “difficult summer”, as wet weather moves across the state and heavy rain falls on already-saturated catchments.

A succession of three rainfall systems will bring downpours across large tracts of Australia’s east this week, with parts of inland NSW already hit with showers and thunderstorms.

“It will be a difficult week but even more so a difficult summer and significant flooding is expected,” Premier Dominic Perrottet told reporters on Wednesday.

“Our rivers and dams are full, that creates a significant risk of flooding that creates a risk to people’s lives and properties.

“There will be many challenges as we move through this period of time, but our focus as a government is to save lives, protect property, and our SES volunteers do an amazing job.”

SES crews are working to prepare communities near swollen rivers and dams for the onslaught of rain, the premier said.

He urged people to avoid taking risks and follow SES instructions.

Assistant SES commissioner Sean Kearns is concerned about western and southwestern parts of the state as more rain falls on drenched catchments.

“This is going to impact communities that have already been impacted by floods over the last month or two,” he told ABC TV on Wednesday.

“What we’re going to see is significant amounts of rain, sometimes the monthly rainfall in just a couple of days, if not more.”

The school holidays mean there are a lot of people travelling in areas they may not be familiar with.

“Take heed of conditions, be very mindful about caravan parks and camping grounds, they’re often next to rivers,” Mr Kearns said.

He also warned racegoers heading to Mount Panorama for the Bathurst 1000 this weekend to follow SES directions, amid concerns the Macquarie River faces moderate to major flooding.

A slow moving rain band is tracking east over central Australia, dumping large amounts of tropical moisture over much of western NSW on Wednesday.

The system is bringing heavy showers with clusters of thunderstorms across a large warning area, which extends from Tibooburra in the northeast to Wilcannia and Ivanhoe in central NSW, through to Deniliquin on the Victorian border, and Nyngan in the central north.

Rainfall totals of up to 50 to 70mm are expected with localised falls of up to 100mm possible, with inland towns including Deniliquin, Griffith, Hay, Cobar, Bourke and Brewarrina on alert for possible flooding.

Hazardous surf and swells are expected on the Macquarie, Hunter, Sydney and Illawarra coasts on Wednesday, with strong and dangerous coastal winds developing on Thursday.

A second trough will bring storms, rain and bursts of heavy falls from Queensland to southern Victoria from Thursday night and into Friday.

Finally, a third rainfall system will sweep across southern Queensland, NSW and eastern Victoria on Saturday and Sunday.

Flood warnings are current across numerous inland catchments including the Namoi, Macquarie, Bogan, Lachlan, Murrumbidgee, Murray, Edward, Culgoa, Birrie, Bokhara, Warrego, Paroo, Barwon, Darling, Macintyre and Snowy rivers.

A flood watch has also been issued for rivers closer to the coast, including the Hunter, Hawkesbury and Colo rivers, and Wollombi Brook, with rises expected from Thursday to Friday.

The successive deluges come close to harvest season with the state’s farmers after already facing a number of set backs as they prepare to work through a third consecutive La Nina season.

NSW Farmers Business, Economics and Trade Committee chair John Lowe said the latest deluge could wipe out remaining crops, and there was already extensive flood damage with properties destroyed, paddocks ruined and roads severely damaged.

“Once the skies clear and the floodwaters recede, we’re going to need an enormous, concerted effort to get our infrastructure up to scratch,” he said.

–AAP