Thai authorities are searching for former prime minister Yingluck Shinawatra after she failed to appear for a verdict in a criminal case that could send her to prison for 10 years.

Yingluck’s whereabouts were not immediately known and her absence fuelled speculation that she might have left the country.

An official of Yingluck’s Pheu Thai party, who is close to the Shinawatra family, said she had left Thailand.

Supporters of Yingluck Shinawatra outside the Supreme CourtSupporters of Yingluck Shinawatra outside the Supreme Court (Wason Wanichakorn/AP)

Yingluck, who became Thailand’s first female PM when her party swept elections in 2011, is accused of negligence in overseeing a money-losing rice subsidy programme. She pleaded innocent and said the charges were politically motivated.

A verdict had been expected on Friday, as thousands of Yingluck supporters gathered outside the court and thousands of police stood guard, but Yingluck never appeared and a judge read out a statement saying her lawyers had informed the court she could not attend because of earache.

The judge said the court did not believe the excuse because no official medical verification was provided. He said a warrant would be issued for her arrest, and announced the hearing would be postponed until September 27.

Thai soldiers stand guard outside the Supreme Court(Sakchai Lalit/AP)

Prime minister Prayuth Chan-ocha, the military chief who engineered the 2014 overthrow of Yingluck’s government, said he did not know where she was, but the government was “looking for her”.

“If she’s not guilty she should stay and fight the case,” he said. “If she’s not here, what does that tell you? Will she still say that she didn’t get justice?”

Defence minister Prawit Wongsuwan said security forces had not allowed Yingluck to leave and were checking possible routes she might have used. He said security officials had not seen her leave her Bangkok home in the last two days.

The trial 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 a 2006 coup.

Former Manchester City owner Thaksin ShinawatraFormer Manchester City owner Thaksin Shinawatra (Martin Rickett/PA)

Thaksin, who has lived in Dubai since fleeing a corruption conviction he says was politically motivated, has avoided commenting on his sister’s case.

When Yingluck’s government proposed an amnesty in 2013 that could have absolved her brother and allowed him to return without being arrested, street protests erupted that eventually led to her government’s demise in the 2014 coup.

The junta that seized control of Thailand has since suppressed dissent and banned political gatherings of more than five people. The long-awaited decision on Yingluck’s fate has rekindled tensions in the divided nation, but the military remains firmly in charge.

Fearing potential unrest, authorities tried to deter people from turning out on Friday by threatening legal action against anyone planning to help transport Yingluck supporters.

A supporter of Thailand's former Prime Minister Yingluck Shinawatra displays a picture of her outside the Supreme Court(Gemunu Amarasinghe/AP)

Thousands of people turned up outside the Bangkok courthouse anyway, along with thousands of police who erected barricades around the court.