At least 50 people have fled the cafe , Seven Network video shows . Police negotiators are in contact with a hostage taker , the report says . Hundreds of police officers have shut down a usually bustling area in Australia 's most populous city amid the crisis . Australia 's government says it 's unclear whether the attack is politically motivated . Local media carry images of police holding a black box with Arabic writing .
At least 50 people have fled the cafe , Seven Network video shows . Police negotiators are in contact with a hostage taker , the report says . Australia 's government says it 's unclear whether the attack is politically motivated . Local media carry images of police holding a black box with Arabic writing .