Dozens of homes on the NSW mid-north coast have been evacuated after a septic tank system leaked sewage into yards and streets.

The Local Emergency Operations Controller (LEOCON) issued an evacuation order for residents at Stuarts Point, north of Kempsey, late on Friday night.

The spillage, likely caused by heavy rainfall and flooding, forced residents at 45 homes to flee their properties.

In a statement, LEOCON said the health department confirmed there was a major health risk for anyone who came into contact with the water over concerns it was full of bacteria.

The area was declared a danger and evacuated immediately.

"At this time, Ocean, First, Second, Third, Fifth, Seventh and Ninth avenues are in the declared zone" the statement read.

"The evacuation operation has commenced and multiple agencies are now in the area to assist residents.

"Vehicles outside the contaminated area can be moved but occupants must undergo decontamination and evacuation registration prior to departure."

Fire and Rescue NSW worked with police to evacuate 32 residents.

They were given gumboots before being hosed down and ushered onto a waiting bus.

Residents were then taken to a nearby youth camp as emergency crews started door knocking to make sure locals were not experiencing any signs of illness.

"Residents are being advised they must stay in their home, as personnel from NSW Fire and Rescue doorknock all affected homes and advise of arrangements for a compulsory evacuation tonight," police said in a statement.

The evacuation order may be in place for seven to 10 days.

Meanwhile a central coast council has closed all its public beaches and warned people not to go swimming amid fears of flooding and contamination.

"Please do not swim in our beaches and waterways," the council warned in a Facebook post.

"Following six days of heavy rain and flooding across the coast, we have made the decision to close all central coast beaches and ocean baths until Tuesday."

The council said prolonged torrential rainfall increased the risk of the waterways being polluted due to stormwater which could be a "hazard to your health".

"While it might be tempting to take a dip in the ocean or one of our coastal lagoons, waterways, rivers and lakes - please steer clear," the council said.

An update will be provided next week.

NSW Health also issued a warning on Friday against swimming in floodwaters because of the unpredictable current, submerged objects and contamination.

Two people have died during the flood disaster, one in NSW and one in Queensland, and there are fears for an elderly woman, who has been missing for more than a week after he car was discovered submerged in floodwaters near Port Macquarie.

Originally published as Residents evacuated in flood aftermath