"The blast of a shotgun has connected with the side of his elbow."
It was not clear how far away the two men were from each other, "but if you take precautions you shouldn't accidentally shoot anyone", the spokesman said.
Wellington Free Ambulance spokesman Daniel Paul said the injury was "pretty serious".
The man was flown to Wellington Regional Hospital by helicopter and had surgery on his elbow on Saturday afternoon.
He was in a stable but serious condition, said Wellington Hospital spokesman Matt Paterson yesterday.
Hastings-based duck shooter James Buckrell said gun safety was "the most important thing" to consider when duck shooting.
"The biggest thing is to treat every firearm like it's loaded," Mr Buckrell said.
"I think some people can get a bit complacent. It also comes down to clarifying what your target is and who's behind it."
The arrested man will face a charge of careless use of a firearm causing injury and has been bailed to appear in the Masterton District Court at a later date.
Later on Saturday another duck hunter was shot in the buttocks and leg while hunting in Glenorchy, northwest of Queenstown.
The man, also in his 40s, had minor wounds and told Queenstown police they were caused by pellets ricocheting off some- thing. Nicole McKee, Firearms & Hunter safety programme manager at the Mountain Safety Council (MSC), said shooters had to be vigilant about safety precautions.
"Duck hunters need to ensure that their firing zone is always checked before they pull the trigger.
"They need to look at the area between them and their target, as well as beyond their target.
"At the end of the day, a shot has been fired and it has hit the guy in the elbow."
The duck shooting season lasts four to eight weeks, depending on the region.
In the lead-up to the season, both police and the MSC stepped up publicity around safety shooting practices.
Senior Sergeant Matthew Morris of the Wellington District Command Centre reminded the public that firearms should always be handled in a safe manner and even a momentary lapse could lead to serious injury or death.
- Additional reporting APNZ
