Police in the western Athens district of Egaleo were on standby Saturday after a dispute between two Roma families left one person dead, another injured and two properties seriously damaged.
The vendetta began on Friday after a 21-year-old man rammed two men with his car, killing a 45-year-old and sending a 31-year-old to hospital.
Police said the driver and the 31-year-old had earlier been involved in a brawl with the driver of the car, raising suspicions that the former deliberately aimed for him with his vehicle but also hit the second man.
Police said the 45-year-old victim was not connected to the previous argument.
The driver allegedly went on the run following the incident.
Meanwhile, later on Friday, a group of about 100 people set fire to a shop owned by the elusive 21-year-old.
A few hours later, another group set fire to a house that belongs to a relative of his.
A riot police squad has been dispatched to the area to prevent fresh violence. Authorities said investigations would continue.