Thousands of farmers drove their tractors to Berlin's famed Brandenburg Gate on Tuesday in a mass protest against new environmental regulations they say threaten their livelihoods. 

Long convoys brought traffic to a standstill in the heart of the city's government district, in the biggest display yet of farmers' anger over agricultural policy changes agreed by Chancellor Angela Merkel's cabinet in September.

"First the plants starve, then the farmers, then you," read one sign attached to a green tractor. 

"Do you know who feeds you?" read another.

The government's policy package includes plans to limit the use of fertiliser to tackle nitrate pollution in groundwater, and phase out the controversial weedkiller glyphosate by 2023 to protect insect populations.

Furious farmers say the environmental protection measures go too far and pose an existential risk to their farms.

Many are also fed up with the "farmer bashing" they say has cast them as villains in the fight against climate change.

Police said more than 5,000 tractors rolled into Berlin for the four-wheeled protest, leading to convoys as long as 20 kilometres on some roads.

Other German cities have seen similar demos in recent weeks, including a large one in Bonn last month. 

Farmers have also taken to the streets in France and the Netherlands with similar complaints.

Germany's agriculture minister Julia Kloeckner defended the government's measures, aimed in part at bringing the country in line with EU regulations, but said she understood the farmers' frustrations.

"Consumers keep expecting farmers to do more, but are increasingly less willing to pay more for it," she told ARD broadcaster, calling for more appreciation for the industry.

Kloeckner was due to address the rally later on Tuesday, where farmers plan to hand her a large envelope containing letters expressing their grievances.

Merkel has invited some 40 agricultural organisations to the chancellery for talks on December 2.