The main opposition candidate challenging Belarusian strongman Alexander Lukashenko demanded a fair election as she cast her ballot in the presidential poll on Sunday.

"I really want the election to be honest, because if the authorities have nothing to fear, if all the people are for Alexander Grigoryevich (Lukashenko), then we will agree with that," Svetlana Tikhanovskaya said as she cast her ballot in the capital Minsk.

The 37-year-old English teacher and translator's campaign has emerged as the biggest challenge in years to Lukashenko, who has ruled the ex-Soviet country of 9.5 million since 1994.

She stood for election after authorities barred her husband, popular blogger Sergei Tikhanovsky, from running and then jailed him.

Tikhanovskaya's campaign office said Sunday that one of her key allies, Veronika Tsepkalo, had left the country for Russia out of concern for her safety.

Presidential candidate Svetlana Tikhanovskaya casts her ballot in Minsk
Presidential candidate Svetlana Tikhanovskaya casts her ballot in Minsk AFP / Sergei GAPON

Tsepkalo, whose ex-diplomat husband Valery Tsepkalo was barred from standing in the election, had backed Tikhanovskaya in the campaign and her husband had already fled to Moscow fearing arrest.

"We have been in contact with Veronika Tsepkalo. She says she is in Moscow and will vote there," the press service for the campaign said.

"We respect Veronika's decision, the situation is not easy. Everyone has the right to assess their personal risks on their own."

Tsepkalo and Maria Kolesnikova, campaign chief of ex-banker Viktor Babaryko who was also dropped from the polls and is in jail, joined forces with Tikhanovskaya to mount a united campaign against Lukashenko.

Photographs of the three women standing together and making their signature gestures -- Tikhanovskaya's punched fist, Kolesnikova's fingers in a heart shape and Tsepkalo's victory sign -- have become an emblem of the opposition.

Kolesnikova was briefly detained on the eve of the vote on Saturday.