(CNN) Ten young football players were killed and three others were hurt when a fire broke out at a training center of Brazilian football club Flamengo, authorities said.

Firefighters responded to reports of a blaze early Friday at the training center in Rio de Janeiro, where flames engulfed a dormitory where the players were sleeping.

An aerial view shows Flamengo's training complex where an early morning fire left 10 people dead.

Flamengo is one of Brazil's biggest and most popular clubs, playing their home matches in Rio de Janeiro.

Rio Gov. Wilson Witzel announced three days of mourning to remember the victims, state-run news agency Agencia Brasil reported.

The derby between Flamengo and bitter Rio rivals Fluminense -- one of the biggest matches on the Brazilian calendar -- was scheduled for Saturday at the Maracana stadium, but has now been postponed.

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