The big winner was the right-wing populist BoerBurgerBeweging (Farmer-Citizen Movement), or BBB, garnering some 19% of votes, according to preliminary results published by broadcaster NOS overnight.

First official results were expected on Thursday.

The farmers-led party has gained popularity as a voice opposing the government's proposed environment regulations to cut nitrogen emission levels. Farmers have protested the measures for several years, at times using violence.

Around 13 million Dutch citizens were called to vote in the election that determines the parliaments of the country's 12 provinces. The vote also indirectly decides the composition of the Senate, or upper house, of the national parliament.

According to the projections, the governing coalition only garnered about a third of the 75 seats in the Senate.

Observers believe the election results could threaten the stability of Prime Minister Mark Rutte's coalition. It is now doubtful whether his government can still push through important laws on agricultural reform, climate protection and asylum policy.

Politicians do not rule out a government crisis if the coalition loses significant support in the Senate.

Rutte, who has been prime minister since 2010, expressed his disappointment following the initial forecasts. "This is not the victory we had hoped for," he said.

BBB chairwoman Caroline van der Plas meanwhile said voters had sent a clear signal. "You can no longer ignore us. We will enter government," she said.

At the local level, the provinces decide on road construction and transport policy, as well as environmental protection and housing construction.

Especially in rural areas, BBB gained ground and could become the strongest force. The party, a first-time participant in the provincial elections, only has one seat in national parliament.

Dutch citizens also voted for the composition of the country's water management authority on Wednesday, the results of which are expected by next week the earliest.