Denmark's Social Democrats, led by Prime Minister Mette Frederiksen, have finished first in the general election but posted their weakest showing in more than 120 years, with the left-wing bloc failing to secure a majority.

With all votes counted in metropolitan Denmark, the left bloc has been credited with 84 seats in the 179-seat parliament and the right with 77, while 90 are needed for a majority.

The centrist Moderate party, headed by Foreign Minister Lars Lokke Rasmussen, has emerged as kingmaker with 14 seats, with negotiations expected in the coming weeks to form a coalition government.

Frederiksen, who has been in office since 2019, told supporters she was "ready to take on the responsibility of serving as Denmark's prime minister again for the next four years".

She added that "there is little to suggest that forming a government will be easy."

Lokke called for a cross-bloc coalition.

"We must not be divided. We must not be red (left-wing). We must not be blue (right-wing). We have to work together," he said.

Coalition partner Troels Lund Poulsen of the Liberal Party ruled out forming a new government with the Social Democrats.

"Either we have a centre-right government, or we go in opposition," he said.

Far-right gains

Frederiksen, seen as the favourite ahead of the vote, said her party had expected losses.

"We were expecting to lose ground, that's normal when you run for a third time," she said. "Of course I wish we would have gotten more votes."

The Social Democrats secured 21.8 percent of the vote, their lowest since 1903.

The anti-immigration Danish People's Party more than tripled its support to 9.1 percent.

"A tripling of votes is a remarkable expression of the Danish people in support of my party," leader Morten Messerschmidt said.

Frederiksen said the result showed continued backing for strict migration policies.

"We must control the number of people coming here," she said.