As the boy's aunt and brother panicked, the crew took control.
Mr Tuki said the child was being held upright and was choking on his own blood so they put him in the recovery position. He and the brother held the boy while Mr Batt - who has extensive St John training - used bandages from the crew's first-aid kit to put pressure on the wound.
The boy's aunt was on the phone to emergency services but too upset to speak so Mr Wehipeihana took over.
"You could see she was extremely distressed so it was easier just to take the phone off her," he said.
The men played down their efforts, but Mr Wehipeihana said Mr Batt had shown maturity beyond his 18 years, keeping a level head as he administered first aid until emergency services arrived after about 10 minutes.
They described the initial moments after they ran to the scene as gruesome and scary, and yesterday morning did not want to listen to news reports in case their efforts had been in vain.
To their relief the boy was alive in Christchurch Hospital in a critical but stable condition.
The dog has been put down.