Bangkok:  Thailand's Supreme Court has issued an arrest warrant for former prime minister Yingluck Shinawatra after she failed to turn up to hear the verdict in her trial on negligence charges on Friday.

Ms Yingluck faces up to 10 years in jail if found guilty in her handling of a rice subsidy scheme for farmers when she was in power.

Ms Yingluck's lawyers told the court country's first female prime minister was unwell.

But lead judge Cheep Chulamon said "the court does not believe she is sick…and has decided to issue an arrest warrant". The judge ruled she might be a flight risk.

The ruling date has been rescheduled to September 27.

Thai media reported the court has seized the equivalent of $1.1 million that Ms Yingluck had posted as bail.

The arrest of Ms Yingluck, 50, would stoke anger among her Red Shirt supporters who see the charges against her as a witch-hunt. 

Thousands of supporters defied a government ban on gatherings of more than five people and threats of legal action to converge on the court. Many were from her rural heartland in the country's north and north-eastern provinces.

"Yingluck, fight, fight fight," many shouted.

Ms Yingluck had told her supporters on the eve of the hearing to stay home, fearing people with "ill-intentions" might and try and cause trouble for her movement.

"I want all of you to give me support by staying at home and monitoring the news to avoid any risk of unexpected incident by people with ill-intention against the country and us," she wrote on Facebook.

The military government put its credibility on the line by pursuing the first charges against a former prime minister over a flawed government policy.

The generals who toppled Ms Yingluck's democratically-elected government in 2014 knew they risked her becoming a heroine in the eyes of millions of Thais if she was found guilty and jailed.

No corruption allegations were made against her in the case.

Prosecutors alleged Ms Yingluck's government ignored numerous written warnings from the Auditor-General and the country's anti-corruption commission about the program's risks and irregularities.

Ms Yingluck told the court she did not terminate the program because it was never intended to generate revenue but to raise the incomes of farmers, and she forwarded the warnings to the relevant government agencies.

A subsequent investigation found no irregularities, she said.

Thailand's deputy prime minister Prawit Wongsuwan told Reuters he could not confirm whether Ms Yingluck is still in Thailand.

"She could be ill at any hospital. She could be ill,"  he said. "It is not clear whether she fled."

Even before Friday's scheduled verdict authorities had hit Ms Yungluck with a $US1 billion ($1.2 billion) fine over the program and seized her 16 bank accounts, which prompted a public outcry.

Other former governments have implemented similar subsidy schemes but the one Ms Yingluck promised during an election campaign in 2011 spectacularly collapsed with losses to the state of up to $17 billion.

The plan was to buy up local rice harvests for as much as 50 per cent above market rates to drive up global prices.  But the market saw it as a clumsy attempt at price manipulation.

Thailand amassed huge rotting stockpiles of rice rather than sell at a loss overseas.

The case is the latest in a decade-long offensive against a largely rural-based mass movement supporting a political machine founded and directed by Ms Yingluck's elder brother, former prime minister Thaksin Shinawatra, who was toppled in a 2006 military coup.

Mr Thaksin, a telecommunications tycoon, fled into exile in 2008 to escape a prison sentence on a conflict of interest charge he claims was politically motivated.

Critics had predicted that Ms Yingluck too would flee overseas before Friday but she appeared calm in the days leading to the verdict, making merit at Buddhist temples. Reporters camped outside her residence in Bangkok said she had not been seen since Wednesday. 

The online news site Khaosod English quoted  a source close to Ms Yingluck saying she had left the country for Singapore on Thursday. The claim could not be verified.

Thitinan Pongsudhirak, director of the Institute of Security and International Studies at Bangkok's Chulalongkorn University, said it was clear enough that politics was involved in the trial.

"I mean, this is a government that was elected in 2011 by a simple majority and it had a policy platform led by the rice pledging scheme," he said.

"The scheme led to losses probably, but on the other hand, if we use this benchmark for other governments, then we could have a lot of government leaders in jail."

Professor Thitinan said the only way for Thailand to break a vicious cycle of coups, changing constitutions and elections is for retooled charter rules and laws to be determined by electors.

"Otherwise the recent past of protests, confrontation and turmoil will return to haunt and keep Thailand stuck," he said.

The Bangkok Post said in an editorial the case reveals how Thailand's justice system is prone to be dragged into political turmoil.

"The case against Ms Yingluck, prosecuted under the ruling regime which ousted her, is highly political," the newspaper said.

Since the 2014 coup, Thailand has become one of south-east Asia's most repressive countries with political gatherings banned, strict censorship of the media and hundreds of activists, journalists, academics and former politicians detained or charged.

Prime Minister Prayuth Chan-ocha, who led the coup, urged Thais to accept the court's ruling.

"Please keep this like any other. Generally those who are guilty must be tried in courts," he told reporters.

Mr Prayuth has promised to allow a return to democracy but has repeatedly delayed setting a date.

"In the next period, democratic mechanisms must take over. I confirm no attempts will be made to stay in power," he said.

"If I want to enter politics, I must turn into a politician."