People have been ordered to evacuate parts of Maclean before the floodwaters of the Clarence River peak in the northern NSW town.

Upstream the city of Grafton escaped major flooding on Tuesday when the river peaked just below the levees.

The State Emergency Service (SES) issued a Flood Evacuation Order for parts of Maclean at 5.34pm on Tuesday based on the Bureau of Meteorology's predicted flood peak.

The SES is urging people in named streets in Maclean not to delay their evacuation, warning they could be trapped and may need rescuing.

"Remaining in flooded areas is dangerous and may place your life at risk," it said.

The SES urged evacuating residents to move and stay with family or friends, or make other accommodation arrangements.

It says an assembly area will be established at the Maclean Showground where residents can get information on temporary accommodation and other help.