Areas around the Gwydir River, which is predicted to deliver major flooding, received huge falls on Wednesday, with 94mm recorded at Delungra and 76mm near Narrabri in the North West Slopes.

Bureau of Meteorology senior meteorologist Jane Golding says that's more rain than Narrabri would typically receive for all November.

NSW Emergency Services Minister David Elliott says the SES has received more than 190 calls for help since the deluge began on Wednesday.

Fast-rising rivers and flash flooding have led to six flood rescues, with the bulk of the SES calls coming from northeastern NSW, as well as storm-related calls from Sydney.

SES deputy commissioner Daniel Austin says the SES was "heartened" by an incident near Narrabri on Wednesday afternoon that showed people were heeding repeated warnings not to drive through floodwaters.

About 5.30pm an empty school bus and three 4WDs, including one with children inside, were caught on road between two creeks that had risen quickly.

"Those people stayed in place and chose not to drive through those floodwaters," Mr Austin said.

"They called emergency services and we worked together to get those people out ... that's a really positive outcome that highlights what you can do and what you shouldn't do: driving through floodwaters."

A rescue took place near Bingara about midnight, with four SES crews ferrying up to 30 visitors at a flooded caravan park out of danger, Mr Austin said.

"This is a fast-moving event in places, the risk is not just from the long, slow rainfall, but these sharp short thunderstorms," Mr Austin says.

"People across NSW have had a couple days of warning ... we're asking people across the whole state to take that into account and be prepared," he said.

Australian Associated Press