A monument to the sinking was unveiled at Ocean Beach in 2011, and the memorial will be the focus of Saturday's ceremony.
A 5am dawn blessing by local iwi, in which the navy's Maori Culture Group will take part, will be followed by an 11am ceremony at the HMS Puriri memorial attended by members of the navy's mine disposal unit, the Littoral Warfare Unit.
The ceremony is part of the navy's Operation Neptune 75th anniversary calendar and will be attended by Whangarei mayor Sheryl Mai, Merchant Navy representatives, including veterans, and family of the late Lt Blacklaws.
Director of Operation Neptune, Captain Andy Watts, said the ceremony was particularly relevant for the Littoral Warfare Unit, which conducts mine clearance operations in the Pacific Islands.
"A key role of the navy's Littoral Warfare Unit is to identify and clear mines to ensure waterways are safe for the shipping that carries 98 per cent of New Zealand's imports and exports by volume," he said.
"It's important also to note the role of the Merchant Navy in sustaining New Zealand's national life during World War II. This commemoration highlights that the relationship between the RNZN and the Merchant Navy is just as important now as it was 75 years ago."
Heritage NZ representatives will also be at Saturday's ceremony.
"The memorial faces out to sea where the Puriri was sunk after hitting a mine while carrying out minesweeping operations with another ship, HMS Gale," Heritage New Zealand's Northland manager Bill Edwards said.
"The explosion must have been huge as the ship sank so quickly no lifeboats were able to be launched.
"Five sailors were drowned as a result, including the ship's commanding officer, two stewards, a stoker and an able seaman." The 26 survivors were rescued from the water by the Gale.
