Violent clashes erupted between police and protesters in Istanbul on Wednesday, when hundreds tried to breach barricades and reach the city's main square to mark May Day in defiance of a government ban.

Some demonstrators hurled stones, gasoline bombs and fireworks at riot police, who responded with tear gas as clashes broke out on side streets leading to Taksim Square.

The square is the city's main hub and is currently undergoing a major facelift. The Turkish government banned celebrations at Taksim this year, citing construction safety risks.

Trade union groups, however, have vowed to mark May Day in Taksim, which is of symbolic importance to workers and left-wing groups. Dozens of protesters were killed there in 1977 when unidentified gunmen opened fire on May Day celebrators.

On Wednesday, subway, bus and ferry services across the Bosporus were partially suspended and bridges were closed down to prevent large groups from gathering in Taksim. Some 22,000 officers were deployed to police the city, the state-run Anadolu Agency reported.

Throngs of demonstrators, waving flags and shouting anti-government slogans, still tried to access the square.

The Istanbul governor's office said 20 protesters were arrested and at least two police injured during the clashes. The private Dogan news agency said at least two journalists were also hurt.

Wednesday's clashes in Istanbul came after three years of relatively peaceful May Day festivities.

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Associated Press writer Suzan Fraser in Ankara, Turkey contributed.