A Kapiti teenager is on life support in Wellington Hospital after being found unconscious in a Paraparaumu shopping mall carpark, police say.

The 17-year-old was found behind the KFC restaurant at Coastlands around 3am on Saturday. He underwent surgery in Wellington Hospital and was now in a critical condition, Detective Inspector Mike Johnson said.

It was too early to say how he was injured or whether weapons were involved but early inquiries indicated he was involved in an altercation with a group of people outside the nearby Retro Bar before 3am.

"From there, the male has then gone through an alleyway which leads to Coastlands," Det Insp Johnson said.

The alleyway and KFC carpark had been cordoned off.

Police would like to hear from anyone who was at the Retro Bar and witnessed an argument or saw the victim unconscious.

The teenager was wearing a blue and beige checked shirt with a white T-shirt underneath, blue jeans, light brown boots and a black woollen hat.