Thailand's Constitutional Court dismissed Prime Minister Paetongtarn Shinawatra from office on Friday for an ethics violation, ending her tenure after just one year and delivering another blow to the Shinawatra political dynasty that could push the country into a new phase of unrest.

Paetongtarn, who was Thailand's youngest prime minister, is now the sixth leader from the billionaire Shinawatra family or backed by it to be removed by the military or judiciary in a two-decade struggle for dominance between the country’s rival elites.

In its verdict, the court said, Paetongtarn violated ethics in a leaked June telephone call, during which she appeared to kowtow to Cambodia's former leader Hun Sen when both countries were on the brink of an armed border conflict. Fighting erupted weeks later and lasted five days.

The ruling paves the way for parliament to elect a new prime minister, though the process may be drawn out, with Paetongtarn's Pheu Thai party losing bargaining strength and struggling to hold together a fragile coalition with only a narrow majority.

The decision ends the premiership of the daughter and protégé of influential tycoon Thaksin Shinawatra. Paetongtarn, 39, had little political experience when she was suddenly elevated to leadership following the dismissal of her predecessor, Srettha Thavisin, by the same court a year ago.

Paetongtarn has apologised over the leaked call and said she was trying to avert a war.

She is the fifth premier in 17 years to be removed by the Constitutional Court, underlining its central role in the protracted power struggle between Shinawatra-led governments and a powerful network of conservative and royalist generals with far-reaching influence.

The focus now shifts to who will replace Paetongtarn, with Thaksin expected to be at the centre of negotiations between parties and power-brokers to try to keep Pheu Thai at the head of the coalition.

Deputy Prime Minister Phumtham Wechayachai and the current cabinet will serve in a caretaker role until parliament elects a new prime minister, with no fixed deadline for when the vote must take place.

There are five eligible candidates for the position, but only one from Pheu Thai, Chaikasem Nitisiri, a 77-year-old former attorney general with limited cabinet experience who has kept a low profile in politics.

Other leaders include former Prime Minister Prayuth Chan ocha, who has retired from politics after leading the 2014 coup against a Pheu Thai government, and Anutin Charnvirakul, a former deputy premier who withdrew his party from Paetongtarn’s coalition after the leaked call.

The ruling plunges Thailand deeper into political uncertainty at a time when the public is frustrated with stalled reforms and an economy that the central bank expects to grow by only 2.3 per cent this year.

Any Pheu Thai-led government would rely on a coalition with only a slender majority and could face constant challenges in parliament from an opposition with strong public support that is pushing for an early election.

"Appointing a new prime minister...will be difficult and may take considerable time," said Stithorn Thananithichot, a political scientist at Chulalongkorn University.

"It's not easy for all parties to align their interests," he said. "Pheu Thai will be at a disadvantage."