NSW police are urging motorists to slow down on Christmas Day as wet weather affects much of the state.

NSW Traffic and Highway Patrol Commander, Assistant Commissioner John Hartley, urged motorists on Tuesday to slow down to avoid a tragedy.

"With rain predicted for much of the state today, I want motorists to slow down and drive according to the conditions," he said in a statement.

"We often see an increase in traffic incidents during wet weather, but I'm hoping all motorists heed the warning."

The warning comes as stormy weather hit parts of NSW due to a southerly change.

Mr Hartley said 203 people had been injured in 621 crashes on the state's roads since Friday, compared to 158 people injured in 530 crashes the same time last year.

He said police had conducted 148,945 breath tests and laid 231 charges in the first four days of Operation Safe Arrival.

On Christmas Eve, police caught 717 motorists speeding and issued 993 infringements for other traffic offences.

An elderly woman's road death on Sunday was the first recorded in NSW this holiday season.