Prime Minister Kyriakos Mitsotakis is poised to win the most votes in Greece’s general election on Sunday, but he’ll likely fall short of the threshold to form a government on his own, raising the prospect of another election in about a month.

Mitsotakis’s center-right New Democracy party got just over 40.8% of the votes with almost 90% of them counted, outperforming expectations. Support for the leftist Syriza party of former Premier Alexis Tsipras was about 20%.

Voters appeared convinced by Mitsotakis’s pledge to build on one of the European Union’s fastest economic recoveries that has Greece on the cusp of a return to investment grade. The three top parties will have about nine days to see if a coalition is possible, but all the main group leaders have ruled out working with each other and Mitsotakis has indicated his preference for a one-party government.

“New Democracy has the people’s approval to rule alone,” Mitsotakis said Sunday night, adding that the result was a political earthquake. “The people want a strong government with a four-year horizon.”

Sunday’s election was the first under a new proportional representation system that effectively means that a candidate needs around 48% of the vote to be able to form a single-party government. If a second election is held, the winner will get as many as a 50-seat bonus, meaning that threshold falls to about 38%, depending on the number of parties that qualify for the 300-seat parliament.

The election was overshadowed by several incidents that weighed on Mitsotakis’s campaign in the run-up to the vote. These included a train crash earlier this year that left 57 people dead and a scandal in which the prime minister confirmed that his intelligence agency spied on an opposition candidate.

But voters were particularly focused on Greece’s economic transformation, which has seen gross domestic product recover to just about where it was when Greece defaulted on its debt in 2010. Unemployment has more than halved from its peak of 28% and the country’s stocks and bonds have soared.

The risk premium on Greek government bonds compared with Germany’s has fallen by about a third over the past year. They trade with a similar yield to Italian bonds. The rebound in the economy has set the nation on track to recover its investment-grade status after 13 years.

The Socialist Pasok party got 11.6% of the votes counted; the Communist party was at 7.1%; the far-right Greek Solution at 4.5%. The other parties failed to reach the threshold to enter parliament.

Mitsotakis is a strong advocate of one-party governments, but he has said that he would try to form a coalition government if that’s what the outcome of the vote suggests is the will of the people.

Pasok’s leader Nikos Androulakis — who was one of the people spied on by the Greek secret service during Mitsotakis’s administration — has so far ruled out any cooperation that will lead to a government under either Mitsotakis or Tsipras.

Starting Monday, Mitsotakis will have three days to see if he can form a government. If he fails, the mandate to try to secure a majority in parliament goes to the second party for another three days, and if that also fails then the third party will also have another three days to negotiate a possible administration.

If all efforts are unsuccessful then the president can invite all party leaders to explore the possibility of forming a grand coalition. If this attempt also fails — or if the president decides not to initiate the process — then Greeks will be called to vote again in about a month.

Mitsotakis called for the process to be accelerated in order to arrive at a stable “government solution.”

(Updates with results, Mitsotakis quote in fourth paragraph.)