Clashes between ex-rebels and armed civilians killed six people in Bangui as anger mounted over abuses by the Central African Republic's new rulers, police and medics said on Saturday.

The violence broke out on Friday in a northern neighbourhood of the capital when a student believed to have been kidnapped by ex-rebels was found dead, a police official said on condition of anonymity.

"Protesters, most of them youths, set up barricades and started burning tyres on the street to voice their anger over the discovery of the body of a student... who was abducted in broad daylight by Seleka forces," he said, referring to the former rebel group now in power.

The police source said the ex-rebels then "opened fire on the protesters with live bullets, killing one person."

Shots were fired back at the Seleka men, killing two, the official said, adding that another three unidentified people were shot dead in the ensuing confusion. Twenty five people were also wounded.

"This is a provisional toll that is likely to worsen because gunfire from heavier and automatic weapons was heard in the neighbourhood later on, soon spreading to much of the city," he said.

Seleka (which means "alliance" in the Sango language) forces ousted the impoverished country's leader Francois Bozize in March.

One of its leaders, Michel Djotodia, has since been sworn in as interim president but smouldering violence has continued to plague the landlocked nation.

"The wounded keep coming in. Most of them were hit by stray bullets in various Bangui districts," Romain Guitizia, the director of a Bangui hospital, told AFP.

"It's tense here, we're not sure what is going to happen," he said.

Witnesses said a Protestant youth centre and a bank were looted as chaos spread across the capital.

Residents have repeatedly taken the law into their own hands over what rights groups say are executions and pillaging by ex-rebels.

Relief agencies in the Central African Republic warned on Thursday that the troubled nation was facing a serious humanitarian crisis as a result of the coup and its aftermath.

Human Rights Watch said Seleka had "targeted and killed at least 40 civilians, and intentionally destroyed 34 villages or towns since February."

Djotodia's administration denies any involvement in the violence but senior Seleka members, including one of the former rebellion's top generals, issued a statement demanding an internal dialogue to tackle ongoing insecurity and rights violations.

Bangui has asked the regional bloc CEMAC to boost its troop presence from 700 to 2,000 in a bid to stabilise the capital.

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