Around 50 people are thought to have died with many more injured.
Thousands of people have been killed and hundreds of thousands displaced in the auto since mainly Muslim Seleka rebels ousted President Francois Bozize in 2013.
Fighting has broken out in the Central African Republic (CAR), a day after a ceasefire was signed between rebels and the government.
Thirteen of the 14 armed groups signed the agreement Monday that called for an immediate cease-fire.
Town Mayor Maurice Belikoussou told Reuters that 42 bodies had been taken to hospital. An estimated 41,000 people there have fled for their lives.
But clashes between former Seleka members and anti-balaka fighters erupted early in the morning in Bria, around 580 km (360 miles) northeast of the capital Bangui.
"The priority now is a cease-fire", said Vlad Monteiro, a spokesman for the United Nations peacekeeping mission.
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He has said he grew up in the district and now lives close to Emory University, where his fiancée attends medical school. She pointed voters instead to her "proven conservative record " as a state and local elected official.
The UN says that the country is facing a dire humanitarian crisis. However, other reactions in the capital Bangui were less optimistic.
Central African Republic has been mired in violence since 2013 and at least half a million people are internally displaced.
President Faustin-Archange Touadera said he is counting on the support of the global community to help bring stability.
"(This accord) simply follows the same scenario repeated over and over", said Joseph Bindoumi, president of the Central African League of Human Rights.
"It is those who sign them who don't respect them".
BBC West Africa correspondent Thomas Fessy says deals have been signed in the past few years but all have failed to bring the country back to peace and stability. "The accord is signed at a time when violence is on the increase in the east of the country and the civilian population is desperate for the violence to stop". "The armed groups should cease the hostilities and put an end to people's suffering". The Seleka group has splintered into factions, some of them fighting each other.
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