Two Greek TV stations said the youth was rushed to a hospital but died upon arrival.
The news enraged hundreds of youths in the area who began rioting by attacking other police cars with stones and firebombs.
Police responded by firing tear gas at the crowd, evacuating some restaurants in the area, and closing several streets to all traffic.
A few hours after the rioting began, the youths appeared to divide into at least three separate groups and there was a lull in the fighting.
At least one teenager was arrested, but no casualties were reported among the rioters or police.