Protests greet G20 leaders in Hamburg, Germany

July 7 (UPI) -- Police in Hamburg, Germany, used water cannons on protesters who said they were provoked into violence on the sidelines of the G20 summit of world leaders Friday.

Demonstrations across the city on Thursday turned to violence, and dozens of police officers were reported injured. Friday's protests were smaller and more dispersed, but equally disruptive, The New York Times reported.

Police said demonstrators threw paving stones and bottles at them. Officers responded with pepper spray and jets of water, though protesters said they were provoked into conflict by police wearing riot gear. Among the more than 100 officers injured, at least five required hospitalization, including a helicopter pilot who said he was blinded by a laser. Protest organizers said some of the estimated 12,000 demonstrators were also injured but a casualty count was not available.

Police said they arrested at least 29 people amid the protests, though did not specify charges.

Police advised travelers to avoid the area near Hamburg's major rail station where they said people had set cars afire and Molotov cocktails were thrown on Thursday.

On Friday morning, protesters gathered on street corners to block G20 leaders from traveling to Hamburg's convention center, as police helicopters flew around the city. Members of a group called "Color the Red Zone," a reference to an area near the summit site off-limits to demonstrations, told CNN they were attempting to make travel to the talks difficult.

Police pushed away small groups of marchers blocking the streets. Injured demonstrators, who were told they were in areas closed to protest, were recorded recovering from possible pepper spray or tear gas attacks, CNN reported.

The two-day summit of the world's 19 largest economies, and the European Union, formally begins Friday. The first face-to-face meeting between U.S. President Donald Trump and Russian President Vladimir Putin is expected Friday.