Thousands of western NSW residents have evacuated their homes as the Lachlan River neared 11 metres for the first time in decades, while emergency services enlisted support from New Zealand, Singapore and the US to manage the state’s ongoing flooding catastrophe.

Major flood warnings are current in NSW and Victoria, and flood watches are active for parts of Tasmania, where severe weather and snow down to 700 metres into Wednesday is forecast.

Heavy storms this week brought falls of 120 millimetres of rain from the Blue Mountains to NSW’s far west, causing significant damage to roads, bridges and transport infrastructure. Forbes, where residents have been evacuated, endured 118mm of rain in the 24 hours to Monday morning. Up to 600 homes and businesses are expected to experience inundation.

"This is our time of need … which is why we’re calling upon international flood rescue crews for the first time,” NSW Minister for Emergency Services and Resilience and Minister for Flood Recovery Steph Cooke said.

“The flooding we continue to experience has been unprecedented and requires an unprecedented level of support.”

Flood operations are expected to continue for several more months as 24 New Zealand flood rescue operators head to NSW at the request of the State Emergency Service (SES), which is also working with authorities in Singapore and the US to secure additional support.

Australia’s highest rainfall total over the week to Monday was at Mount Hotham in Victoria with 204mm. The wet weather has since eased but burgeoning river systems continue to rise.

“The catchments are full, the rivers are full, the ground is wet," NSW Premier Dominic Perrottet said. "It doesn't take much rainfall for flash flooding to occur.”

SES Commissioner Carlene York said all national resources had been “exhausted” and international support was needed. So far this year, the SES has responded to more than 72,000 requests for assistance and 3400 flood rescues.

About 150 people were rescued on Monday from roofs in Eugowra and Molong, with support from 160 emergency service personnel and 14 helicopters.

"The velocity was extremely fast - too fast in many cases to put boats in the water,” SES Chief Superintendent Dallas Burnes told Channel Nine.

The Bureau of Meteorology says major flooding continues along several rivers in NSW. At Forbes, which just over a week ago experienced record flooding that damaged homes, businesses and roads, the Lachlan River may reach around 10.80 metres - levels similar to the mid 1952 flood. Further rises are possible depending on dam outflows and upstream peaks.

Major flooding is already occurring at Cowra and Nanami and continues at Condobolin, with further rises possible, and is expected at parts of the Murrumbidgee River, including at Hay.

The NSW SES is working to resupply communities isolated by flooding in Collarenebri, Walgett, Lightning Ridge, Goodooga, Brewarrina and parts of Bourke across an area of about 40,000 square kilometres – more than half the size of Tasmania.

People in the southern border town of South Albury and those at Western Plains Tourist Park in the central west have also been ordered to evacuate. The Wyangala dam is spilling at record levels, with 230,000 megalitres being released a day, exacerbating flooding along the Lachlan River.

The Insurance Council of Australia (ICA) says there are 14,481 claims so far from flooding since October 12, mostly property claims in Victoria.

ICA has previously said there have been almost $9 billion in insured losses from floods since drought broke in early 2020. Flooding in northern NSW and Queensland at the start of the year was one of only three Australian catastrophes to exceed $5 billion in insured losses, in normalised currency terms.