China allows no public discussion of the events of June 3 and 4 1989, when soldiers backed by tanks and armoured personnel carriers fought their way into the heart of the city, killing hundreds of unarmed protesters and onlookers.
The government has never issued a complete, formal accounting of the crackdown or the number of casualties.
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Cloud and outbreaks of rain will ease away eastwards during the morning, clearing the east coast around midday with sunny spells developing.
Police and emergency services are attending the scene.
Rebel-held east remains at risk while the pumping station supplying the western part of the city is once again in operation.