A Marlborough Sounds watchdog group says it's time that Tory Channel was closed to all shipping and an alternative inter-island route put in place before the arrival of the new, larger passenger ferries in 2024.
The narrow, rocky gap which passenger ferries ply daily is considered one of New Zealand's most tricky areas to navigate.
Guardians of the Sounds says Kiwirail's proposed new ferries will be about 50 metres longer than the current ships, and that will pose problems.
Peter Beech told RNZ Nelson-Marlborough reporter Tracy Neal there is an alternative through Queen Charlotte Sound, and they want the ferries to use it.
Maritime New Zealand says it's committed to working with all groups to ensure any potential risks are managed.