A motorist and a police dog handler narrowly avoided being injured by a man swinging a Samurai sword wildly in the middle of a road in Upper Hutt.

Inspector Shane Cotter said police were called after a motorist reported swerving to avoid an attack from the 31-year-old Silverstream man's blade in Reynolds Bach Dr about 3.40am yesterday.

''He had a samurai sword in his hand and he was swinging it around striking the road causing it to spark,'' Cotter said.

''A member of the public drove past and saw him take a swing. Fortunately it missed.''

When a police dog handler arrived at the scene they were also attacked by the man, he said.

''The police dog handler retreated into his vehicle and got his dog out.

''With the use of the dog the sword was removed from the man.''

The man was this morning in Hutt Hospital undergoing surgery on serious bite wounds to his leg.

Police do not know why the man was standing on the road with the sword.

''We can't say for sure, but I'd say he was under the influence of some sort of drugs,'' Cotter said.

''[The samurai sword] seems to be the weapon of choice for people on P (methamphetamine).''

The man had been charged with possession of an offensive weapon, assaults with a weapon and resisting police and was scheduled to appear in the Upper Hutt District Court on Thursday.

The Independent Police Conduct Authority would investigate the incident because of the serious injuries the alleged offender suffered in the incident.

- © Fairfax NZ News