Tens of thousands of people have protested in Congo, calling for the resignation of President Joseph Kabila once his term ends in December. Opposition leaders fear Kabila may try to extend his rule for a third term.

Demonstrators chanted anti-government slogans and waved flags as they marched down Kinshasa's streets on Sunday, calling for President Joseph Kabila to resign after his term ends in late December.

Addressing tens of thousands of protesters, opposition leader Etienne Tshisekedi said the electoral commission needed to be convened by September 19, the "first red line, which must not be crossed."

"The electoral body must be convened for the presidential election. If it is not, high treason will be proved in the person of Mr. Kabila, who will take responsibility for the misery of the Congolese people," said the 83-year-old leader.

Presidential polls are due to take place in November, but Kabila's government has said logistical problems may delay the vote.

In May, Congo's Constitutional Court ruled Kabila could remain in office in caretaker capacity beyond the end of his mandate. The ruling sparked fears that Kabila could try to extend his rule by a third term.

Tshesekedi credited with uniting opposition

Kabila, 45, took over as president of the country of 71 million people after his father was assassinated in 2001. He won a 2011 election against Tshisekedi, which critics say was marred by fraudulent practices.

Earlier this week Tshisekedi returned from Europe, where he had been undergoing medical treatment for two years. An immensely popular figure, he rose to prominence in the 1980s as a strong critic of former dictator Mobutu Sese Seko. Today, Tshesekedi is credited with uniting the voice of the opposition in the Democratic Republic of Congo.

Tshisekedi has also demanded an end to "arbitrary judicial cases" against opposition leaders like Moise Katumbi, who was sentenced in absentia to three years in jail for property fraud, making him ineligible to contest the upcoming presidential poll.