A man wielding a samurai sword who allegedly swung at a passing motorist in the Hutt Valley is in hospital with serious dog bites after he then allegedly swung the blade at the police officer and dog sent to arrest him.

The man, 31, was reported to have swung the sword at the motorist on the road leading up to the Silverstream landfill early on Sunday morning, Inspector Shane Cotter told NZ Newswire.

A dog handler responded and the man allegedly attacked the officer before he could get out of the car.

However, with his dog he was able to subdue the man and arrest him before backup arrived. The man suffered serious dog bites to his thigh.

He has been charged with possessing an offensive weapon, assault and resisting arrest.

Insp Cotter said police did not know what the man was doing there at the time, as there are no inhabited houses nearby.

He would not say if the man was believed to be on drugs.

"But it's not a normal behaviour to be doing what this person was doing," he said.

Insp Cotter said the use of a sword was concerning.

"There've been a number of incidents around the country where people using P have had swords.

"I'm not saying this chap was on P because we don't know that, but it does seem to be a weapon becoming more and more common, unfortunately."