LISMORE has copped more than double its average March rainfall in a single day, with 308mm of driving rains now helping to overwhelm the Wilson River and the city's protective levee.
The northern NSW town's main city street has been transformed into a rushing waterway, with police rescuers already having to brave the torrent to pluck a man to safety he became stranded on a fence.
At least 11,000 in the city are also without power as destructive winds continue through Friday.
Throughout March 2016, Lismore received 139mm, less than half the amount dropped on the town on Thursday and into Friday.
The wettest March endured by Lismore in the past 15 years was in 2009 when 251mm fell on the city, or 50mm less than what fell on the town overnight.
The deluge has forced emergency services to conduct 130 flood rescues overnight, amid warnings that some may die before the waters subside.
NSW SES Deputy Commissioner Mark Morrow said "there could be some very distressing news" as emergency services venture throughout the city.
The unprecendented rains have pushed the Wilson River over the top of the city's $18.9 million levee that stretches 3km and rises more than 11.5m high.
The waters were not enough to top the levee in 2009, when waters reached 10.4m
That was the closest the levee had come to being overcome, until today.
Floodwaters in the town are now topping 11.53m and are thought to be rising.
The city's warning siren sounded at 4.15am, the first time in 12 years, as water flowed into the city's CBD and residents were told to flee.
Where the rain fell (in 24 hours to 9am Friday)
Byron bay - 233
Coffs Harbour 126mm
Evans head 287
Grafton Airport 86mm
Mullumbimby - 362
Tweed Heads -196