Elderly NSW man on mobility scooter struck

An elderly man riding a mobility scooter has been critically injured in a collision with a vehicle in Sydney's southwest.

The 89-year-old was crossing a road in Greenacre just before 7am on Wednesday when his scooter was struck by a Toyota Hilux.

He was taken to Liverpool Hospital, where he remains in a critical condition with a head injury.

The Hilux driver, a 21-year-old man, was taken for mandatory blood and urine testing.