The police said later in a statement that 72 policemen and 11 protesters were injured after tear gas was fired to stop an "unauthorized" demonstration in the city.
Masked protesters attacked policemen by throwing stones, it noted.
Nasser Zefzafi, the jailed leader of the protest movement, called before his arrest in late May for a massive demonstration on July 20, the anniversary of a famous battle between the region and Spanish colonial forces in 1921, Xinhua news agency reported.
The situation in Al Hoceima has been tense since October 2016, when fish vendor Mouhcine Fikri was crushed to death after climbing into a rubbish lorry to retrieve his swordfish confiscated by police.
The demand for justice for Fikri in the northeastern region has evolved into a major grassroots movement to require greater government investment to create more jobs.
Morocco has not witnessed any protests of this size since the pro-democracy demonstrations during the Arab spring (massive public protests in middle-eastern and North African Arab states) in 2011.