The Rena captain and second officer pleaded guilty in Tauranga District Court today to 10 of the 11 charges laid over the grounding of the container ship.
The men were charged following an investigation into the ship's collision with Astrolabe Reef off Tauranga on 5 October.
A week later Maritime New Zealand charged the men with operating a vessel in a manner causing unnecessary danger or risk, which carries a maximum penalty of $10,000 or a maximum term of imprisonment of 12 months.
In November, MNZ laid further charges against each man relating to the discharge of harmful substances from ships or offshore installations.
The following month they were also charged under the Crimes Act, alleging they wilfully attempted to pervert justice by altering ship documents after the grounding.
Each charge under the Crimes Act carries a maximum penalty of seven years' imprisonment.
In court today the captain entered guilty pleas to all six charges laid against him, and the second officer pleaded guilty to charges laid under the Maritime Safety and Crimes Act, but entered no plea to a charge laid under the Resource Management Act.
The men's identities remain suppressed.
They are due to be sentenced at Tauranga District Court on May 25.