A secondary school in the Southwest Region was targeted for "murderous attacks by unidentified individuals," CRTV news channel said.

In addition to the four dead, several people were being given hospital treatment, it said.

"The defence and security forces are currently carry out a sweep to search for the assailants," it said.

Roger Kaffo Fokou, secretary of the National Union of Secondary School Teachers (SNAES), told AFP that "three students were shot dead. A wounded teacher also died while she was being taken to hospital."

"Armed men arrived at the school. They opened fire and threw explosives into the classrooms," the head of a local civil society group told AFP.

Cameroon's Southwest and neighbouring Northwest regions are home to English-speakers who comprise around a fifth of Cameroon's 22 million people.

Years-long grievances over perceived discrimination at the hands of the francophone majority flared into a declaration of independence on October 1, 2017.

Armed separatists launched attacks on the security forces, triggering a violent crackdown.

The spiral of bloodshed has claimed more than 3,500 lives and forced around 700,000 people to flee their homes, according to monitors.

NGOs say that killings of civilians and abuses have been committed by both sides.

Separatists frequently attack buildings deemed to be symbols of the francophone state, including schools and teachers, whom they accuse of "collaboration" with the government in Yaounde.

On October 14, anger flared in Buea, the capital of the Southwest Region, after a policeman killed a schoolgirl and was lynched by a mob.

The presence of the anglophone regions is a legacy of the colonial era in western Africa.

The former German possession of Cameroon was partitioned after World War I between Britain and France.

In 1961, part of the British territory, the Southern Cameroons, joined French-speaking Cameroon after it gained independence from France.