Drivers are being urged only to travel if journeys are “absolutely necessary” after snow, ice and freezing rain hit parts of East and West Sussex.
Several key routes had been affected by the weather on Wednesday evening, including the A23 and A27, Sussex Police said.
Officers said there had been “multiple collisions” in parts of Brighton and Hove.
East Sussex County Council added people should “stay at home if possible”.
The council said gritters had been out since 15:00 GMT.
Some drivers on social media reported abandoning their vehicles due to heavy snowfall making journeys treacherous.
A yellow weather warning for snow remains in effect for the region until 23:59.
The Met Office is anticipating 2cm-5cm (0.7-1.9 inches) of snow falling, with 3cm of snow measured in Herstmonceux.
It warned of travel disruption caused by the snow and said some vehicles and passengers could become stranded.
The weather service also said power cuts were likely, while delays and cancellations to rail and air travel were expected.
