Tens of thousands of people are marching in the Algerian capital, Algiers, in the latest protest against President Abdelaziz Bouteflika.
The demonstrations – now in their third week – were triggered by the ailing president’s decision to seek re-election for a fifth term in April.
Mr Bouteflika has ruled Algeria for 20 years but has rarely been seen in public since he had a stroke in 2013.
He has warned that the protests could plunge the country into “chaos”.
In a letter published by Algeria’s official APS news agency on Thursday, the 82-year-old leader urged “vigilance” against “domestic and foreign” forces that might infiltrate the demonstrations.
But he also praised the demonstrators for “peacefully expressing their opinions”.
How big are the latest protests?
The protest on Friday is thought to be the largest yet in a series of demonstrations that began three weeks ago.
Riot police, equipped with water cannon, have been deployed along the protest route, and helicopters have been spotted circling the capital.
Demonstrations have also been reported in Algeria’s second-largest city, Oran, and Tizi Ouzou.
Some organisers had called for 20 million people to take part in Friday’s demonstrations, billed as the “#March 8 Movement” on social media.
The privately owned Arabic-language news website, El Khabar, quoted the public transport body for Algiers as saying that all bus, tram, train and metro services had been suspended ahead of the rally.
Reuters news agency quotes the private Ashourouq TV station as saying that several lawmakers from the governing FLN party have resigned to join the protesters.
Opposition politicians have also been meeting to discuss the protests, according to BBC North Africa correspondent Rana Jawad. However, she says, the opposition has long been weakened by the FLN and is viewed with a certain suspicion by the public.
What do the protesters want?
The wave of protests were triggered by the announcement last month that Mr Bouteflika would seek a fifth term in office.
Mr Bouteflika later released a statement saying that he would step down early if re-elected – but this has not placated the demonstrators.
Many young Algerians are frustrated by a lack of economic opportunity and by what they perceive as the corruption of an elite that has governed the country since it gained independence from France.
Banners at Friday’s protest carried slogans saying: “Algeria is a republic, not a kingdom”, and “No elections till the gangs are brought down”, Reuters reports.
Where is the president?
The president is believed to have been transferred to a hospital in Switzerland on 24 February, for what his campaign described as “routine” medical tests.
His campaign manager told El Khabar on Thursday that his health raised “no concerns”.
A spokesman for the Geneva University Hospitals (HUG) refused to comment when asked if Mr Bouteflika was there. However, he has been quoted as saying that it had received 1,500 phone calls on Tuesday after the president’s location was revealed by French television programme Quotidien.
While most of the calls have reportedly been enquiring about the president’s health, a number of videos posted to social media show prank calls from Algerians.