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Many residents of some of Rio de Janeiro's worst slums are fleeing their homes to escape a drug war that has left part of the Brazilian city in ruins, and killed a dozen people.

Smoke rose from the smoldering wreckage of a police helicopter shot down by drug gangs Saturday, while eight buses burned and gunfire filled the air in the slum of Morro dos Macacos.

Police say the fighting broke out early Saturday when one of the city's three main drug gangs invaded the area in an attempt to expand its territory.

Ten suspected gang members were killed in subsequent gunbattles with police.  Several people were injured.

Two police officers riding in the helicopter were killed.  Police say the aircraft exploded on a football field after the pilot tried to make an emergency landing with the aircraft in flames.  Four people on the helicopter managed to escape the flames. 

Hundreds of police officers were sent into the area to end the fighting.

The outbreak of violence comes just weeks after Rio won the right to host the 2016 Olympic Games.

Rio has long been known for its high crime and murder rates, and has more than 1,000 slums or shantytowns, known as favelas.

Some information for this report provided by Reuters, AP and AFP.