Germany is set for weeks or even months of protracted coalition talks after the race to produce a successor to Angela Merkel after 16 years in power failed to produce a clear winner, with the centre-left Social Democrats and the centre-right conservative alliance in a tight first and second.

Exit polls and early counted results put the Social Democrats ahead by just a wafer-thin majority and both its chancellor candidate, Olaf Scholz, and his rival Armin Laschet of the CDU/CSU insisted they had earned the right to form a government.

The Green party, in jubilant mood after securing its best result in a national poll, despite having lost the lead it held early on and dropping about 13 points since April, was confident of becoming a kingmaker in the upcoming coalition talks.

Both its candidate, Annalena Baerbock, at 40 the youngest chancellor candidate by some way, and the SPD’s Scholz expressed their willingness to work together, with Scholz quickly moving to congratulate the environmentalists and saying there were plenty of areas in which the parties overlapped.

But he said in the so-called “elephant round”, a television debate involving all the lead candidates two hours after polling booths closed, “out of respect for the citizens of this country, we cannot make any final decisions”. Scholz said his wish was for “constructive discussions, so that the whole country can recognise itself in the future government”.

The initial reaction of the Social Democrats (SPD) had been of cautious optimism as well as relief that Scholz, the incumbent finance minister, appeared to have retained gains made in the latter part of the campaign. At the headquarters of the Christian Democrats (CDU), any relief that it had not slipped as low as polls suggested it might under Armin Laschet was overshadowed by the fact that it appeared to be heading for its worst result in a federal election.

The Green party was also buoyed by having doubled its result compared with 2017, and beaten the pro-business Free Democrats (FDP) into third place. The results strongly indicate that the environmentalists are on track to enter a new government.

Likely constellations include a so-called green-yellow-red “traffic light” coalition, with the SPD, Greens and FDP, or a “Jamaican” coalition of the CDU/CSU, Greens and FDP.

According to the results, compiled for German broadcasters by pollsters, the SPD was on 25%-26%, the CDU/CSU alliance on 24%-25%, with the Greens on 14.5%-15% and the FDP on 11%-12%.

The far-right Alternative fur Deutschland party (AfD) is poised to re-enter the Bundestag for the second time, having gained 11%, while the leftwing Die Linke appeared to have just managed to reach the 5% hurdle required to earn a place.

The preliminary results indicate that Germany is heading, as was widely predicted, for a three-way coalition. If past experience is anything to go by – in 2017 it took around three months – this will involve an extended period of heated wrangling. Merkel would remain as a caretaker leader in the meantime.

The election marked the first time since the second world war that an incumbent chancellor did not run for re-election. It left the contest far more volatile and unpredictable than ever, and left many Germans – according to polls, between 25% and 40% – undecided up until the day of the vote.

Laschet, addressing disappointed CDU followers at the party’s Berlin headquarters in the presence of Merkel, said the party had suffered from not having the so-called “chancellor bonus” after the latter’s departure. “It was clear to us that without having the bonus of being home to the person in office, it would be an open, hard and close election campaign,” he said.

“We are not happy with the result,” he added, but earned cheers for saying he would nevertheless put his “every effort into ensuring the new government is CDU-led”. Merkel looked on and waved, her face largely covered by a black mask.

The SPD minister Hubertus Heil told a German broadcaster: “The night is young. But it’s a huge success for us. A year ago we were 20% behind the CDU, but now we’re neck and neck.” He added he was “damned proud” of his party.

Baerbock called the result “wonderful”. “We held an election campaign that we’d never had before,” she said, addressing party members in Berlin, flanked by her co-leader, Robert Habeck. But, she added: “We can’t just cheer – we wanted more.” She admitted to mistakes, which she said were her fault, at the start of the campaign, but added: “We have a clear task for the future” – pledging to help create what she called a “climate government”.

Katrin Goring-Eckhardt, a leading Green party politician, said that even if her party had hoped for a better result – it was once polling at 27% – it was celebrating a success. “This is the vote of a generation that wants change,” she said, pointing out that many younger people had voted for the party.

“The task ahead is far bigger than any election,” she added, referring to the challenge to tackle the climate emergency, and promised that in government the Greens would deliver on the party’s promise for 100% of German energy to come from renewable sources.