A Royal New Zealand Navy sailor is in North Shore Hospital in Auckland in a critical condition following an incident at Devonport Naval Base on Monday night.
In a statement NZ Defence Force say the sailor was taking part in advanced diver training in about six to eight metres of water when the incident happened.
Immediate first aid was given at the scene by his colleagues and emergency services were called. WorkSafe has been nofiited.
"The RNZN is providing support to his family and colleagues," the statement reads.