In Dhaka, protesters held red banners and flags chanting "Hang the killers, Hang the Factory Owners" after the devastating collapse of a garment factory, as rescuers warned the final toll could be more than 500.
At a mass in the Vatican, Pope Francis condemned as "slave labour" the work conditions of the victims of the collapse, who were making clothes destined for high street retailers in the West.
In Turkey's biggest city Istanbul, police fired tear gas and water cannon at stone-throwing protesters trying to gather for a banned demonstration.
Clashes erupted in three neighbourhoods leading to Taksim Square -- a traditional hub for leftist May Day protests -- where the authorities had blocked off the streets.
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"Death to fascism. Long live May 1," shouted the protesters who were rallying to calls of defiance from leftist parties and unions.
The Turkish government had banned May Day gatherings on the square blaming renovations.
By midday tension had abated and the protesters slowly dispersed as protests in other parts of the massive Turkish city went without incident.
In neighbouring Greece, a strike stopped ferry services and disrupted public transport in Athens as workers went on the march against austerity in a country where the jobless rate reached 27.2 percent in January.
Police said 13,000 protesters had assembled in Athens and Thessaloniki.
Unusually, hard-pressed businesses stayed open to allow for shopping in the run-up to Orthodox Easter on Sunday.
In Spain, where the government has so far managed to avoided a full blown international rescue, unions called for 82 protests across the country.
Spanish unemployment is at a record 27.16 percent and union UGT called on workers "to make perfectly evident the total failure of the austerity policies ... Which in our country is confirmed in the facts."
Unions in France, the second biggest economy in the eurozone, marched divided with union leaders in disagreement over government efforts to make the French work code more flexible.
As recession continues to sap the eurozone and wider EU, the Eurostat data agency yesterday reported unemployment across the eurozone climbed for the 23rd consecutive month -- hitting a record 12.1 percent in March.
At the Vatican, Pope Francis urged political leaders to fight unemployment in a sweeping critique of "selfish profit".
"Not paying fairly, not giving a job because you are only looking at balance sheets, only looking at how to make a profit. That goes against God!" he said in his strongly-worded address.