At about 3pm today Police received a 111 call from members of the public concerned about a man's behaviour in Levin.
A Police officer arrived and attempted to arrest the man.
Initial information indicates that during the arrest process both the officer and the man fell to the ground, with the man hitting his head.
The officer called for medical assistance for the man.
The man is now in Wellington Hospital where he remains in an induced coma.
The area where the incident occurred has been cordoned off and a critical incident investigation is underway.
"This has been a distressing incident for all those involved and our thoughts are with this man and his family," says Acting Central District Commander Inspector Belinda Dewar.
"We are mindful that an investigation into the circumstances is in the very early stages and as such we are not able to provide any further detail at this time."
The Independent Police Conduct Authority will be notified.
