AMSTERDAM -- Dutch police shot at a tractor during a heated night of farm protests and detained three demonstrators, the latest incident in a string of protests against government plans to cut pollutant emissions that many farmers fear would hurt their livelihoods.

Police in northern Friesland said Wednesday that no one was hurt in the incident that involved warning shots and direct targeting of a tractor that broke free from a line. Police said there was an attempt to drive into their vehicles and officers.

Because shots were fired, an official investigation into the incident was started.

Dutch farmers angry at government plans to slash emissions have blocked roads and supermarket distribution centres for several days, sparking fears of food shortages.

The unrest among Dutch farmers was triggered by a government proposal to slash emissions of pollutants like nitrogen oxide and ammonia by 50 per cent by 2030. Provincial governments have been given a year to formulate plans to achieve the goal.

The reforms are expected to include reducing livestock and buying up some farms whose animals produce large amounts of ammonia. Farmers argue they are being unfairly targeted and are being given no perspective for their future.