An independent Egyptian trade union leader says hundreds of workers from several provinces who came to hold a meeting in Cairo for International Workers' Day have been prevented from assembling by police.

Kamal Abbas, of the Center for Trade Unions and Workers' Services, says some 650 workers were in the city center Sunday seeking an alternate location to hold their conference after police prevented them from entering the journalists' syndicate building.

The area is currently under lockdown by police vehicles and barricades, dozens of uniformed and plainclothes officers and armed security troops, some wearing facemasks and carrying automatic weapons.

The journalists' syndicate has been a rallying point for demonstrations in the past, and was blocked in a similar way for planned protests against government policy last Monday.