Masked protesters smashed bus shelters and set fire to rubbish bins. AFP reported around 100 arrests.
Security has been high in Strasbourg and across the German border in preparation for Friday's summit.
Some 25,000 police are on duty to control the tens of thousands of protesters expected to attend.
Groups of youths, many wearing hoods or scarves, walked through a suburb of the city carrying banners saying:
"Stop repression in London and Strasbourg".
Bus stops and vehicles were vandalised, shop windows smashed and a barricade put up on one street.
One protester rammed a pole through the front window of a police vehicle.
A passenger in the car appeared to be holding a handgun as it quickly reversed.
In a separate incident, AFP reported that a German photographer had been taken to hospital after being injured
in the stomach by a rubber bullet
lol, idiot with a gun
sangwria 2 years ago