Algerian authorities halted train and metro services in the capital Algiers on Friday amid heavy security ahead of expected protests against President Abdelaziz Bouteflika.
Mass demonstrations now entering their third week have posed the biggest challenge to the ailing 82-year-old president, who has ruled for 20 years and is standing for re-election on April 18.
Tens of thousands of Algerians, tired of the dominance of elderly veterans of the 1954-1962 war of independence against France, have been demanding that Bouteflika step down, but despite ill health, he has submitted his candidacy papers.
Mass protests are expected to start in the afternoon.
On Thursday, Bouteflika issued his first warning to protesters, saying the unrest could destabilize the country.
The president has not spoken in public since suffering a stroke in 2013, and is currently in hospital in Geneva.
