Several people were injured on Wednesday as Turkish riot police used water cannon and tear gas to disperse hundreds of protesters who defied a May Day ban on demonstrations in a central part of Istanbul.

Several people were injured on Wednesday as Turkish riot police used water cannon and tear gas to disperse hundreds of protesters who defied a May Day ban on demonstrations in a central part of Istanbul.

About a dozen people were hospitalized after exposure to tear gas. Two policemen were among those injured as well as an AFP photographer.

The Istanbul governor's office said 20 protesters had been arrested.

The Turkish government decided to ban May Day gatherings on Taksim Square -- a traditional rallying point -- saying that because of renovations begun in November, security could not be assured for the tens of thousands of demonstrators expected.

But the leftist Disk union vowed to ignore the ban. Turkey has mobilized 22,000 police to provide security throughout the day.

Clashes erupted in three neighborhoods leading to Taksim Square where the authorities had blocked off the streets to prevent protesters from reaching it.

By midday tension had abated and the protesters slowly dispersed. Television stations said May Day was celebrated without incident in two other parts of the massive Turkish city.

Government however authorized the laying of wreaths in memory of 34 people killed during a 1977 May Day protest, when unknown demonstrators fired shots into the air, sparking panic.