The rescue came as thousands of homes in and around flood-hit Lismore are being searched for missing people, with fears the flood death toll of four could rise further.

The rescued family had been stranded with their three-month old and two children aged four and six, with water surrounding their home at Tatham, near Casino, about 23km from Lismore, Fire and Rescue NSW said on Thursday.

The area has just endured its worst-ever flood crisis, with NSW Premier Dominic Perrottet calling the situation in the Northern Rivers "heartbreaking".

The family waved down a passing flood boat crew of NSW firefighters and Victorian SES members who fitted the baby and the rest of the family with life jackets before taking them on board.

They are now safely across the Richmond River at Goonellabah with the children's grandmother.

It was the boat's second rescue for the day after the crew earlier saved three people and seven puppies stranded after a bridge collapse outside Casino.

A dog breeder had become traumatised after flash flooding destroyed the bridge leading to her home on Tuesday, Fire and Rescue NSW said.

The crew reached the woman at her remote home by taking a 5km trek, and used ropes to scale over a 10 metre drop where the bridge had washed away.

Two other stranded people were collected while the dog breeder received medical treatment.

The trio and the litter of seven puppies were taken to safety at a local evacuation centre.

Crews in northern NSW are checking thousands of homes for missing people.

NSW Fire and Rescue Commissioner Paul Baxter says people need to brace for the prospect of more fatalities, after four people were found dead in the wake of the unprecedented flooding.

As the waters began to subside, two women in their 80s and a man in his 70s were discovered dead in their flooded homes, and the body of another man was found floating in a Lismore street.

Police are still working out how many people are missing and Mr Baxter said "some people just haven't been heard from".

Communications remain difficult in Lismore and many people who are unaccounted for may simply have been unable to make contact.

The next step involves emergency workers going house to house and speaking with locals in hard-hit areas to try to find people who have not made contact since the deluge.

"We are talking literally thousands of homes," Mr Baxter said.

The task ahead was "epic", and now included crews from the State Emergency Service, the Rural Fire Service, Resilience NSW and the Australian Defence Force, he said.

"This is a big disaster and it's over such a widespread area. It's going to be hard work."

Lismore Mayor Steve Krieg said the NSW and federal governments needed to listen to residents, after countless homes and business were ruined by the inundation.

"There are plans that have been in place for many, many years to mitigate the flood levels in Lismore," Mr Krieg said on Thursday.

The town is also facing food shortages - most supermarkets were underwater - as well as petrol shortages.

Residents reported ATMs have run out of cash.

Nearby Ballina, which was hit hard by flooding, also has food and petrol shortages and is banking on freight lines reopening on Thursday.

"Many people today in the Northern Rivers and over the last 24 hours have returned home, and they are returning home to heartbreaking scenes," NSW Premier Dominic Perrottet said.

ADF helicopters were being used to drop critical food supplies to evacuation centres and isolated properties.

"The challenge is going to be enormous," Emergency Services Minister Steph Cooke said, saying hard rubbish disposal would be a major challenge.

The road to recovery will be "very, very long".

Australian Associated Press