Opposition leader Felix Tshisekedi was sworn in on Thursday as president of Democratic Republic of Congo, marking the country's first-ever peaceful handover of power after chaotic and bitterly disputed elections.

Tshisekedi, 55, took the oath of office before receiving the national flag and a copy of the constitution from outgoing president Joseph Kabila, who is stepping aside after 18 years at the helm of sub-Saharan Africa's biggest country.

Thousands of Tshisekedi supporters, many of them dressed in white, celebrated the historic event outside the Palace of the Nation, the seat of the presidency.

"We hope that this will be a real change, especially as he has taken power without bloodshed," said Saddam Kongolo, a member of Tshisekedi's Union for Democracy and Social Progress (UDPS).

One of Tshisekedi's first tasks will be to appoint a prime minister in a move which will see him sharing power with Kabila's supporters, who hold an overwhelming majority in parliament.