The people of Forbes are furious that their town could have its main access cut off for up to six weeks, its tourism decimated as the school holidays kick in, while trade with nearby towns turns into a trickle.

The target of their anger is the Newell Highway. The artery of the central-western NSW is no rural lane but a major thoroughfare that ferries goods from Brisbane through NSW to Melbourne, with Forbes at its centre.

But two sections of the highway – one 16-kilometre stretch between Forbes and West Wyalong and another one-kilometre stretch between Forbes and Parkes – flood every time the Lachlan River breaks its luscious green banks.

"The Newell Highway should never be cut off," said Chris Roylance from the Forbes Business Chamber.

"Other smaller roads next to the river can be cut because that is how God set it up, but the Newell Highway – nah, we are over that. That's wrong, time's up, it needs to be fixed."

The NSW government committed $500 million to an upgrade of the Newell Highway last year, but no plans were included for a small elevation of the highway along the two consistently impacted stretches of road.

Roads Minister Duncan Gay said: "The NSW government is investing historic funds into upgrades on the Newell Highway that the local communities have asked for such as overtaking lanes and town bypasses.

"To flood-proof the Newell Highway for a once-in-20-year flood event would cost more than $1 billion - this region is currently experiencing the worst flood event it has seen in more than 60 years.

He said there "does come a point when Mother Nature takes over" and he empathised with those affected.

"I can understand why businesses are doing it tough with the closure of the highway. What we will do is make sure that we do everything possible for that community that is affected and we are doing that," he said.

The government has said the Newell Highway would be closed for three weeks, although Mr Gay said it could be shut for longer. On past experience, small businesses believe six weeks is a more realistic time frame.

"While the road is shut, our income is going to be decimated," said Ali Plummer, who owns a nearby caravan park, the Big4.

"We are just worried about our staff, we rely heavily on them and they rely on us because they are only employed on a casual basis."

Just as residents were mopping up on Wednesday, more bad news arrived.

The Bureau of Meteorology has issued a severe weather warning for Thursday, with winds of up to 70 kilometres an hour and heavy rain due to hit the saturated central western region.

The isolated town of Bedgerabong looks set to be cut off for up to a month before floodwaters recede, and will rely on helicopters to drop off supplies as the township 400 kilometres from the ocean turns into an island.

"It's the last thing they need," said farmer Neil Mattiske, who estimates that he may have lost up to 400 hectares worth of crops. "It's very disheartening, but you have to get over it, you have to get up."

With more rain forecast, Mr Gay urged people driving to NSW from Queensland or Victoria for the long weekend to stick to major highways such as the Hume or New England because emergency service had been "pulling too many people out of flooded areas".

"If you are planning a trip that involves going from one state to another through NSW, stick to the major highways because the centre is out at the moment," he said.