Guy-Brice Parfait Kolélas died in a Medical plane taking him to France for treatment, campaign director, Rodrigue Mayanda said.
Congolese Opposition Leader Guy-Brice Parfait Kolélas Dies From COVID On Poll Day
Few hours before the election, the 61-year-old had appeared in a video posted on social media Saturday, he said,"My dear compatriots, I am in trouble, I am fight death, but nevertheless I ask you to stand up. Go and vote for change. I will not have fought for nothing. Fight for it. I will not have fought for nothing."
The electoral law doesn't annul the election if one of the candidates dies.
Mr Kolélas, who was diabetic, was one of six candidates running against President Denis Sassou Nguesso, 77, who has been in power since 1979, except for a five-year period after losing elections in 1992.
Mr Kolélas had tested positive for COVID-19 on Friday afternoon. He was unable to hold his last campaign in Brazzaville.
He was admitted to a private hospital in the capital, Brazzaville, and it was later confirmed that he had COVID-19.
Congo-Brazzavile has officially recorded more than 9,000 cases of Covid-19 and 130 deaths.
The country has imposed a night-time curfew in the two main cities of Brazzaville and Pointe-Noire and closed its borders due to the pandemic.