More ships will ignore a ban on sailing near to the Poor Knights Islands if the Maritime Safety Authority does not start prosecuting offenders, a marine expert warns.

In December, the International Maritime Organisation declared the Poor Knights Islands a "Mandatory Area to be Avoided" -- a ban requiring ships longer than 45 metres to keep at least five nautical miles east of the Poor Knights.

Despite more than a dozen breaches being reported to the MSA, no shipping companies have been prosecuted.

Northland marine expert Wade Doak said the MSA's weak response had made a mockery of the ban and would lead to more ships breaching it.

"The MSA needs a real shake-up over this. They are playing Russian Roulette with the Poor Knights. There's nothing really we can do to save the Poor Knights if there is an oil spill (caused by a ship breaching the ban)," he said.

"If they won't police this international ban then maybe other aspects of the way the MSA is run need to be looked at. They are charged with maritime safety yet are ignoring a very real threat to maritime safety and it's not good enough."

A network of Tutukaka Coast residents keeps a keen eye on the sea between shore and the Poor Knights to catch any ships breaching the ban. Several regularly report the breaches to the MSA, including sending photos of the offending ships.

As yet, nothing more than a verbal warning has been issued to ships breaching the ban, with the MSA saying it wants time for the rule to become known around the world before it gets tough.

Mr Doak said this slap-on the-wrists attitude was turning the ban into a joke.

"It's now the international law of the sea and there has been enough time for people to get to know about it so start prosecuting," he said.

The MSA said it appreciated the efforts of the Tutukaka community in reporting possible breaches of the zone to the organisation.

MSA deputy director safety and response services Peter Williams said ship owners and masters were given an initial period of grace while the MSA educated them about the zone.

"We are attending ships that have used Whangarei and Marsden Pt and are checking that their navigational charts are up to date, compliant and identify the mandatory area to be avoided.

"On the occasions where ships have been reported inside the area to be avoided we have tracked them to their next port and had our inspectors speak to their masters," Mr Williams said.

"We are now working on better ways to accurately identify and track those ships that breach the area so we can take appropriate enforcement measures."

These measures may include electronic identification in the future.

The area between North Cape and Bream Head, which includes the Poor Knights, is considered to have the second-highest risk factor in New Zealand for oil spills. The area of highest risk is between Bream Head and the Coromandel.