Dozens of English-speaking activists have been released from jail in Cameroon, more than six months after their arrest for organising peaceful protests demanding equal treatment in the mainly French-speaking country.

Fifty-two of them were freed from two prisons in the capital, Yaounde, overnight on Friday and several of the most high-profile activist leaders were released earlier this week following a presidential decree.

Watched by security forces, a crowd of family members and journalists gathered outside to greet the activists.

"I was in jail for five months. My mother couldn't visit me," one freed detainee, who asked not to be named, told Reuters news agency.

"I'm innocent. I was arrested when I went out to see a gathering of leaders ... I was just getting by. Now, I have nothing left."

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Among others freed were civil society leaders Felix Agbor Balla and Fontem Aforteka'a Neba, arrested in January and being held under anti-terrorism laws enacted in response to incursions in the country's north by the Boko Haram armed group.

The pair - who pleaded not guilty in February to charges that included complicity in hostility against the homeland, secession and civil war - had faced a potential death sentence if convicted.

Their case added fuel to long-standing opposition in the Northwest and Southwest regions against President Paul Biya's francophone-dominated government, which has responded to unrest there with a crackdown.

Biya on Wednesday ordered a military court to drop its prosecution of the detainees.

Issa Tchiroma, the government spokesman, said the decision came after dialogue between the government and civil society groups.

But an easing of tensions did not appear imminent as others, including well-known radio broadcaster Mancho Bibixy, remained in jail with their cases due to be reviewed at the end of this month.

"Bibixy and the others were only expressing what they thought. They didn't kill anyone," Calvin Tah Ndangoh, his lawyer, told Reuters. "We do not know for sure why he wasn't released."

English-speaking activists have called for a boycott of the start of the new school year next week.

In response, about 1,000 paramilitary police, including 400 reinforcements, were deployed in the two volatile regions due to the "persistent threat of activists" in a security operation due to last 128 days.