Governor Adolphe Lele Lafrique said Mayor Ngong Innocent Ankiambom of the town of Belo, as well as his deputy mayor and an inspector of basic education, were shot dead as they made their way to the celebrations.
"I will like to express deep concerns and ask the population to remain calm," the governor said, adding that a manhunt had been launched to apprehend and punish the killers.
The officials were shot along a 200-meter stretch between the town council office and the Belo municipal grandstand where celebrations were due to take place, according to a local official who asked not to be named because he was not authorized to speak to the press.
That person said a similar attack was also carried out in the nearby town of Njinkom, but that the number of casualties was not yet known due to communications difficulties.
On May 10, separatist fighters ambushed and killed a commander of a gendarmerie brigade and four of his men in the Central African country's South West region.
Separatists across the North West and South West regions typically step up attacks around National Day, which marks the abolition of the federal system of governance in Cameroon.
This year they said they were imposing a three-day lockdown, restricting the movement of people and cars, in the run-up to the event.
None of the armed groups operating in the region has so far claimed responsibility for Monday's attack. More than 6,000 people have been killed in Cameroon's English-speaking regions since conflict erupted in 2017 after protests were violently suppressed.
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