Tunisia's President Beji Caid Essebsi was taken "seriously ill" on Thursday and transferred to a military hospital, his office said.
An adviser to the president said Mr Essebsi was still alive, despite reports he had passed away.
Tunisia's Prime Minister Youssef Chahed called for people to cease spreading fake news about the president's death, saying he had visited Mr Essebsi in hospital.
"I assure the Tunisians that the President of the Republic is in the process of receiving all the necessary attention he needs," Mr Chahed wrote.
"I call on everyone to refrain from broadcasting false news that will cause confusion among Tunisians," he said.
Mr Chahed reportedly also visited the presidential palace, and the speaker of the parliament called an emergency meeting.
Mr Essebsi was hospitalised last week as well, for what the presidency described as non-serious treatment.
The Tunisian president, 92, said in April that he would not run for re-election in November, saying it was time "to open the door to the youth". Presidential elections are due on November 17, but Mr Essebsi's party, Nidaa Tounes, which he founded, has not found a new candidate.
The country's first freely democratically elected president after the uprising that removed president Zine El Abidine Ben Ali in 2011, Mr Essebsi has been a prominent figure in the country's transition to democracy.
Day-to-day operations in Tunisia are carried out by Prime Minister Chahed, and since the fall of the former president Ben Ali, the presidency has been stripped of influence.
