The leading opposition presidential candidate in the Republic of Congo was receiving oxygen at a private hospital after being diagnosed with COVID-19, a family member said, casting Sunday's election into doubt on the eve of the vote.

Guy Brice Parfait Kolelas, 61, had skipped his final campaign event on Friday after telling some reporters a day earlier that he feared he had malaria. A relative who spoke on condition of anonymity due to the sensitivity of the matter said plans were underway for Kolelas to be evacuated abroad for further treatment.

A video circulating on social media dated Friday showed Kolelas wearing an oxygen mask and with a blood pressure cuff on his arm as he lay in a hospital bed.

“My dear compatriots, I am in trouble. I am fighting death,” the candidate says in a weak-sounding voice after removing his oxygen mask. “However, I ask you to stand up and vote for change. I would not have fought for nothing.”

A campaign spokesman confirmed the authenticity of the video and Kolelas' hospitalization. Two people at the hospital who had seen the Kolelas' test results confirmed to the AP late Saturday that he had tested positive for the coronavirus.

The impact of his illness on Sunday's election was not clear. An article of the Congolese Constitution provides for a postponement if a candidate dies or is unable to participate in the vote.

There was no immediate reaction to the developments from the government or longtime President Denis Sassou N’Guesso.

Kolelas placed second to Sassou N’Guesso in the country's 2016 presidential election with about 15% of the vote. The opposition figure has been particularly critical of the incumbent leader in recent days, declaring that the Republic of Congo had become “a police state.”

Sassou N’Guesso is the third-longest serving president in Africa, ruling from 1979-1992 and then again since 1997 in this nation often overshadowed by its vast neighbour Congo.

The Republic of Congo has had fewer than 10,000 confirmed cases of COVID-19 since the pandemic began, with 134 confirmed deaths.