Lismore flooding: Residents told to evacuate immediately as deaths feared

There are fears people may have died in flood waters in northern NSW, as the city of Lismore floods.

Lennon Bartlett rows a boat to his parents house next door to where he lives in central Lismore. Source: AAP

People may have perished in floodwaters in NSW overnight, the SES fears, as the northern city of Lismore goes underwater.

Flood waters are tearing through Lismore, flooding homes and businesses, as water flows over the top of the city's protective levee, which was raised after previous floods.

The city's siren was activated overnight warning residents to leave immediately.

Flood waters increasing in Chinderah

"It's the first time it's been activated in 12 years," Lismore mayor Isaac Smith told AAP on Friday.

Floodwaters topped the 10.6-metre level at 4.15am on Friday, with water levels predicted to reach 11.5 metres later in the day, Mr Smith said.

Murwillumbah, Chinderah and Kyogle are also expected to be affected by rising waters - more than 19,000 people across the state are subject to evacuation orders.

Lennon Bartlett rows through the McDonald's drive-through in central Lismore, New South Wales, Source: AAP

More than 6000 people have left their homes in northern NSW, as rivers rage with the rain dumped by ex-Tropical Cyclone Debbie, which pummelled Queensland earlier this week.

NSW SES Deputy Commissioner Mark Morrow says there were 130 flood rescues in the NSW area overnight, and fears some who couldn't be reached may have died.

"There could be people overnight that perished in that flood, we don't know at this stage," he told ABC television on Friday.

"We expect this morning that as we start to go out and try to find people that made those calls overnight, there could be some very distressing news."