Thailand's Constitutional Court has dissolved the three biggest parties in the country's ruling coalition and banned the prime minister, along with dozens of top party executives, from politics for five years.

The ruling sinks Prime Minister Somchai Wongsawat's coalition government, made up of six parties. It also raises hopes that thousands of protesters who have for months been seeking the government's ouster will end their siege of the country's two main airports in Bangkok. The siege has stranded thousands of foreigners whose flights home have been blocked.

The court ruled Tuesday that Somchai's People's Power Party, the Machima Thipatai party and the Chart Thai party were guilty of electoral fraud. Somchai and other party executive members were found guilty and banned from politics for five years.

Constitutional Court President Chat Chalavorn said the "court has decided to dissolve the party to set a political standard and an example."

"Dishonest political parties undermine Thailand's democratic system," he said.

Members of the opposition People's Alliance for Democracy protest group at Bangkok's international airport cheered and hugged after they heard news of the verdict.

"My heart is happy. My friends are very happy," said Pailin Jampapong, a 41-year-old Bangkok housekeeper choking back tears as she jumped up and down.

Government spokesman Nattawut Sai-kau said that Somchai and his coalition would step down.

"We will abide by the law. The coalition parties will meet together to plan for its next move soon," he said.

He also said the government was postponing a regional summit in Thailand of Southeast Asian countries, from December to March.

PM expected to remain as caretaker

The ruling sends Somchai and dozens of party executives into political exile, barring them from the country's politics for five years.

But other members of the three parties that escaped the ban can join other factions and try to cobble together a new coalition and choose a new prime minister.

It was expected that Somchai would remain the caretaker prime minister until then.

Thousands of members of the protest alliance have been laying siege to the main Suvarnabhumi international airport and the domestic Don Muang airport for about a week, cutting off all commercial traffic to the capital and stranding more than 300,000 foreign travellers.

At the Suvarnabhumi airport, the verdict was read out on a protest stage outside the main terminal.

"It is good because the [corrupt] politicians have been told to get out. It is good for Thailand. This is a blow for corruption," said Nong Sugrawut, a 55-year-old businessman who was among the thousands camped at Suvarnabhumi.

Politicians banned by the verdict refused to comment. "The court just banned me and my party from political activity so I can't give you any comment," Kuthep Saikrajang, a spokesman of the People's Power Party, said.