Dutch fishermen are blockading the ports of Rotterdam and Amsterdam to protest a ban on cod-fishing imposed by the EU to halt a dramatic slide in cod stocks.
"The entrance to the port of Rotterdam is totally blocked by around 40 vessels," said senior police official Mr Ed Krazewski. The fishing boats are preventing access to both ports from the North Sea.
Mr Krazewski said Dutch authorities were in contact with the fishermen in an effort to end the stand-off but for the moment police had no plans to act against the vessels.
The European Commission closed nearly a third of the North Sea to cod-fishing last month to halt dramatic fall in their numbers.
EU officials say only 70,000 tonnes of adult cod remain in the North Sea compared with 250,000 tonnes in the 1970s.
Cod has historically been the most sought-after fish among Europeans.
AFP