Two dead in separate Sydney crashes

A 59-year-old man and a teenage trail bike rider have died in separate incidents on Sydney's roads.

The man died in hospital after crashing his car into the back of another in Sydney's east.

Police say the four people inside the other car - the 24-year-old male driver and three women aged 25, 62 and 57 - were all taken to hospital with possible spinal injuries after the collision in Double Bay on Saturday night.

It's thought the 59-year-old man may have suffered what police called a "medical episode" before the crash.

Hours later, an 18-year-old man was seriously injured when he was thrown from his trail bike after colliding with a car in Plumpton, western Sydney, in the early hours of Sunday.

He was taken to hospital but died a short time later.