New safety rules in place from 1 July will require every container to be weighed before it is put on board a container vessel for transit anywhere in the world.
If this does not happen, the container will not be allowed to be loaded on a ship.
The new rules stem from fears that shippers sometimes underestimate the weight of their containers to minimise the cost.
This can bring instability and stress to ships at sea, and bring dangers at a port when a container is being unloaded.
Millions of containers are transported across oceans on any one day and a small number of those are lost overboard, creating a shipping hazard for other vessels.
It was not known how many containers fell from ships, and global estimates have varied wildly between 600 and 10,000 a year.
Most containers that did fall, sank, but some remained half-submerged and held up by insulation such as polystyrene.
Those were regarded as particularly hazardous.
The rules were being brought in by Maritime New Zealand following agreement by members of its international parent body, the International Maritime Organisation.
Maritime New Zealand reported last week that 97 percent of New Zealand's trade was transported by sea, and that number was rising.