ALGIERS, Algeria (AP) — Thousands of protesters marched through Algeria's capital Friday against ailing President Abdelaziz Bouteflika's bid for a fifth term, undeterred by volleys of tear gas fired by police during the tense demonstration.

Such anti-government protests are unusual in Algeria, where questions are growing about Bouteflika's fitness for office after a 2013 stroke that has left him largely hidden from public.

Police helicopters circled overhead as hundreds gathered in streets and parks of Algiers after midday Muslim prayer services to join the march. Protesters hoped the protest would send a loud signal of public discontent to the gas-rich North African country's secretive leadership before the April 18 presidential election.

Riot police vans lined the boulevard leading to the presidential headquarters and deployed around the march route.

Soon after crowds started gathering, police fired tear gas on a group of a few hundred coming from the Belcourt neighborhood on the city's Mediterranean shore. It was unclear what prompted the tear gas.

But thousands later marched through Algiers.

Demonstrations were also planned in other Algerian regions, organized via social networks.

Protest organizers issued an appeal for demonstrators to keep calm and stay 2 meters (yards) away from police cordons, to bring families and to clean up after the march.

It's the latest of several protests in recent days against Bouteflika's candidacy for the April 18 election.

The crowds Friday weren't targeting anger just at Bouteflika but at those around him who have kept him, and themselves, in power for so long despite his difficulties in moving and speaking. They feel Algeria's leadership has neglected unemployment, corruption and poverty and ignored public concerns.

They didn't express support for a single challenger in the election, though opposition candidate Ali Benflis expressed support Friday for the march, calling Bouteflika's presidential bid a "humiliation for the Algerian people."

Bouteflika himself, who is 81, is undergoing medical checks in Switzerland.

Bouteflika is credited with reconciling Algerians after a decade of civil war between Islamic insurgents and security forces that left some 200,000 people dead. He has been in power since 1999 and overwhelmingly won re-election in 2014, and most Algerians will likely vote for him again next month for fear of instability that his departure could unleash.