ISTANBUL - POLICE repeatedly used pepper gas and water cannon on Thursday to disperse thousands of workers who prepared to march to an iconic square in Istanbul in defiance of a ban on May Day gatherings there.

Security forces hurled gas grenades outside and into the office of Turkey's main left-wing labour confederation, DISK, in Istanbul's central business and residential Sisli district where a large crowd, most of them workers, gathered early in the morning.

Hundreds of people who had taken refuge inside the eight-storey building crowded the windows to escape the gas, chanting 'Together against the fascists', 'The killer state will be called to account', and 'We are the people, we are right, we will win'.

In the smoke-engulfed street, police sprayed the crowd with crimson coloured water and baton-wielding officers chased demonstrators into the side streets of the busy neighbourhood.

A group of protestors, some of them masked, were seen hurling stones at the security forces.

Several workers were injured and an undetermined number detained, DISK said in a statement, calling the intervention a 'police assault'. There was no comment from the security forces.

Police took similar action against demonstrators who gathered at other points in central Istanbul and chaotic scenes were reported at a hospital where people who suffered from gas poisoning were taken for treatment.

A tear gas grenade went off at the entrance of the emergency room of the Sisli Eftal hospital and tear gas was used to disperse demonstrators outside the building, Mr Ali Carkezoglu, a senior member of Turkey's Doctors Union, told NTV television.

Turkey's three main labour confederations and the government are at loggerheads over the May Day venue, with officials insisting on banning access to central Taksim Square, which has symbolic importance for the country's labour movement and where at least 34 demonstrators were killed on May 1, 1977.

Officials declared Taksim off limits, saying they had intelligence that extremist groups would seek to provoke unrest during the celebrations; the Anatolia news agency reported that police overnight arrested one man in possession of 17 molotov cocktails near Taksim.

The city centre was under a virtual state of siege from the early hours, Taksim Square barricaded by police, cross-Bosphorus ferries cancelled, roads and Metro stations in the area shut down and 66 schools closed for the day.

In addition to several hundred police in riot gear, hundreds of infantry commandos and paramilitary gendarmerie units were positioned in a park overlooking Taksim as helicopters flew overhead.

Television footage showed snipers positioned on rooftops and security forces sealed the entire area to pedestrian as well as vehicular traffic.

Leftist parliament member Ufuk Uras said near Taksim square that the police action was 'unacceptable' and accused the government of 'seeking to deprive workers from their democratic rights with methods left from the Cold War'.

Relations between the government and trade unions were already strained ahead of May Day over an unpopular social security reform parliament passed last month under IMF pressure.

Media reports said more than 30,000 security forces were on duty to enforce the ban on Taksim, the hub of the European side of this city of 13 million.

The 1977 bloodshed took place at a time of severe political tensions and street violence between leftist and right-wing militants in Turkey, which eventually led to a military coup in 1980.

The deaths occurred when unknown gunmen, believed to be far-right militants aided by members of the secret service, fired on a peaceful crowd. -- AFP