Some 10,000 ruling party supporters marched in Bujumbura on Saturday, in a show of unity ahead of a presidential election in June in the central African nation.

Burundi is deeply polarised and tensions are rising, even within the ruling party, because President Pierre Nkurunziza wants to stay in power despite a two-term constitutional limit.

Some 10,000 activists marched in four different processions through the capital, wearing white t-shirts embossed with the logos of the ruling National Council for the Defence of Democracy-Defence Forces of Democracy (Cndd-FDD) party and the Youth League.

They also carried green, red and white balloons, and gathered at a football field near Lake Tanganyika, an AFP journalist said.

With Nkurunziza absent from the rally, marchers chanted his name, while some wore his picture on their T-shirts.

"Recently, some activists took... a party debate that should have remained internal into the public realm," Cndd-FDD President Pascal Nyabenda said, referring to scores of top party members who have publicly opposed Nkurunziza's bid to stay in power.

"We organised this march for peace to show that our party is still united despite these troublemakers, who were only looking out for their own interests," Nyabenda said.

The Cndd-FDD should name its presidential candidate at a conference later this month.

Some 140 top party members recently signed a petition calling on the president not to run. Some 30 of them were subsequently expelled, including Jeremie Ngendakumana, who was party leader from 2007 to 2012.

Opposition and civil society groups in Burundi have branded Nkurunziza's bid to run again as an unconstitutional violation of the Arusha Accords that ended the 1993-2006 civil war.

The president and his supporters have rejected the claims.

"People are afraid of signing the petition because they fear retribution, but many believe that Nkurunziza may lead to our downfall," a Cndd-FDD member said on condition of anonymity.