Emergency services rushed to Link Road, near the Silver Jubilee pub, shortly before 9pm on Sunday.
A blue Vauxhall Corsa, a yellow Mini Cooper, a grey Citroen Picasso and black Ford Focus were involved in the crash.
The driver of the Corsa, a man believed to be in his 20s who lives on the island, was taken to hospital with neck and back injuries.
One woman was taken to hospital after sustaining head and facial injuries.
Paramedics treated two other people at the scene for minor injuries.
A section of the road was closed for two hours while vehicles were recovered and the area was cleared of debris.
Police are still investigating the cause of the accident.