The separatists chose October 1, the anniversary of the official reunification of the anglophone and francophone parts of Cameroon, to declare independence for "Ambazonia", the name of the state they want to create.
Since November, the anglophone minority has been protesting against perceived discrimination.
The government deployed security forces at the weekend in English-speaking regions, notably Buea in the southwest and Bamenda, the main town in the northwest and a hub of anglophone agitation.
Several people were admitted to hospital in Bamenda Sunday after clashes between demonstrators and police, according to a medical source.
"At least one person was injured by live fire" in Bamenda, where the situation was "very tense", a source close to the local authorities told AFP.
The "security forces had to resort to tear gas and sometimes to shots to disperse the protesters", the source said by telephone.
Bamenda residents contacted by AFP reported "shooting" by the security forces without giving further details.
- 'Real bullets' -
One of the leaders of the opposition Social Democratic Front (SDF), Joshua Osih, told AFP the security forces were "firing real bullets at the protesters" but stressed that he was not a supporter of the secessionist movement.
In Ndop, 40 kilometres (25 miles) from Bamenda, two people were "shot dead", according to sources, while one was killed in Kumbo on the sidelines of the protests, city mayor Donatus Njong said.
Also in Kumbo, three prison inmates were shot and killed trying to escape while security forces were mobilised for the deployments in anglophone regions, a source close to regional authorities said.
A young man was shot dead by security forces on Saturday in the southwest town of Kumba, known as a rebellious city since the start of the protests, sparking clashes between security forces and the local population.
"They fired at him during a security operation," a nurse who requested anonymity told AFP. The incident was confirmed by a security source and several local residents contacted by phone.
Cameroon's long-serving president, 84-year-old Paul Biya, took to social media Sunday to condemn "all acts of violence, no matter where they come from or who is responsible."
The European Union called on all sides to be responsible and "respect the rule of law and avoid any act of violence."
The crisis provoked by the protests, which was exacerbated at the start of 2017 when internet access was cut for three months, has intensified in recent weeks with the push to symbolically proclaim independence of the English-speaking regions.
On September 22, "between 30 and 80,000" people demonstrated across Cameroon's anglophone regions, according to estimates by the International Crisis Group (ICG).
- 'No longer slaves' -
The symbolic declaration of independence was made Sunday on social media by Sisiku Ayuk, who describes himself as the "president" of Ambazonia.
"We are no longer slaves of Cameroon," he said.
"Today we affirm the autonomy of our heritage and our territory."
Ahead of the declaration, Cameroonian authorities announced a temporary curb on travel and public meetings across the Southwest Region, adding to a curfew in the neighbouring Northwest Region, also English-speaking.
Internet access has been disrupted since Friday, according to an AFP journalist, despite government assurances that there would be no cutting of access in the anglophone areas.
The majority of Cameroon's 22 million people are French-speaking, while about a fifth are English speakers.
The legacy dates back to 1961, when a formerly British entity, Southern Cameroons, united with Cameroon after its independence from France in 1960.
The anglophone minority has long complained about disparities in the distribution of Cameroon's oil wealth.
Since November, the anglophone minority has been protesting against perceived discrimination especially in education and the judicial system, where they say the French language and traditions are being imposed on them, even though English is one of the country's two official languages.
Most anglophone campaigners want the country to resume a federalist system -- an approach that followed the 1961 unification but was later scrapped in favour of a centralised government run from the capital Yaounde. A hardline minority is calling for secession.
President Biya opposes any such changes.
