The axeman whose axe head flew into a crowd at the Canterbury A&P Show in Christchurch today, seriously injuring a man, is "devastated'', organisers say.

The man, in his 50s, was taken to Christchurch Hospital after the 10.51am incident, which happened during a wood-chopping event.

St John said he was in a "very serious condition''.

Canterbury A&P Show event director Rae Finlay said the incident happened during a tree event, in which axemen cut small pockets into the side of a tall pole and jam a wooden jigger board into it.

They then climb on to the board and chop another pocket, repeating the process until they are several boards up, at which point they chop off the top of the pole.

"Unfortunately the head flew off one of the competitor's axes and hit a member of the public,'' Ms Finlay said.

"The second it happened, all the axemen were over the fence.''

The woodchopping arena was full and everyone acted immediately to help the man and make way for medics and an ambulance, she said.

He was treated on site before being taken away.

"People were very good, people helped.''

A photographer who witnessed the incident was left shaken.

"The guy had climbed the poll and was on his final chops when the head of the axe flew off and into the public. What a thing to happen on the 11th of the 11th - and just before 11 too.''

The competitor whose axe was involved had previously represented New Zealand in the sport.

"He is devastated,'' Ms Finlay said.

"He is one of those people that promotes the sport and supports the young axemen coming through, so it's very sad for all the parties.''

The man would not compete again today but his fellow axemen were carrying on with the programme, albeit minus the tree events. They had had a long break, a safety check and had spoken with Occupational Safety and Health, which was investigating.

"They're all incredibly experienced axemen, they've all been doing it for a very long time and they've never seen that happen before,'' Ms Finlay said.

"But there will be a full investigation into what has happened, to ensure that it can never happen again.''

Canterbury A&P Show woodchopping section convener Gordon Smith said he had been competing for more than 20 years and had never seen a spectator get injured.

"We're all feeling pretty numb,'' he told APNZ.

He was setting up for another event and, when he heard the crowd react, thought one of the axemen had fallen from his pole.

He quickly realised the real problem as all the axemen sprung into action, helping the man and getting paramedics.

"I think it was pretty lucky, there were some doctors in the crowd watching the chopping at the time,'' Mr Smith said.