Yingluck Shinawatra, Thailand's ex-prime minister, has missed a verdict in a negligence trial that could have seen her jailed, prompting the Supreme Court to say it will issue an arrest warrant fearing she is a flight risk, according to the lead judge in the case.

"Her lawyer said she is sick and asked to delay the ruling ... the court does not believe she is sick, " Judge Cheep Chulamon told the court on Friday.

He said the court would seek permission for an arrest warrant for the former prime minister, adding that verdict has been rescheduled to September 27.

Yingluck, who had pleaded not guilty in a case focused on a rice subsidy scheme for farmers, had told the court she could not attend because she was suffering from an ear problem.

"We don't think the defendant is ill," a statement from the Supreme Court judge said. "We think that the defendant is hiding or has fled."

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A spokesman for Yingluck, who was overthrown by a military coup in 2014, declined to comment.

The head of Thailand's immigration police chief, Nanthathorn Prousoontorn, said he believed Yingluck remained in the country.

"Up until this point we have no information showing that Yingluck has exited via any of Thailand's border checkpoints," he told Reuters news agency.

"I believe she is still in Thailand. If she is found she will be arrested," he said.

Yingluck is facing a possible 10-year prison term on charges of negligence linked to an ill-fated rice subsidy programme that cost the state billions of dollars. If convicted, she has the right to appeal.

The case is the latest chapter in a decade-long struggle by the nation's elite minority to crush the powerful political machine founded by Yingluck's brother, Thaksin Shinawatra, who was toppled in another coup in 2006.

Thaksin's removal triggered years of upheaval and division that has pitted a poor, rural majority in the north that supports the Shinawatras against royalists, the military and their urban backers.

The rice subsidies, promised to farmers during the 2011 election, helped Yingluck's party sweep the vote. Critics say they were effectively a means of vote buying, while Yingluck supporters welcomed them and argued that the case against her is politically motivated.

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The long-awaited verdict could inflame tension in the Southeast Asian country and have far-reaching implications in the politically divided kingdom.

Al Jazeera's Scott Heidler, reporting from Bangkok, said hundreds of Yingluck's supporters gathered outside the Bangkok Supreme Court to await the verdict but were not allowed in the vicinity.

"Only media, police and court officials were allowed in this area, normally in the previous court hearings, it was packed with supporters, but this time her supporters are about 200 meters away," he said.

"They believe that she is still here and has not fled the country."

Some of those gathered held roses while others wore white gloves with the word "love" on them.

Supporters of the Shinawatras accuse the ruling generals of political persecution.

The military government has acknowledged it wants to maintain permanent influence over future elected governments, partly through a new constitution that took effect earlier this year.