Dozens of protesters in Beirut have entered the foreign ministry during a wider demonstration over the huge explosion that left at least 158 dead.
Several thousand people are on the streets in a planned protest, but there has been violence. Police fired tear gas at stone-throwing demonstrators.
Sounds of gunfire have also been heard from central Martyrs' Square.
In a televised address, Prime Minister Hassan Diab said he would ask for early elections as a way out of the crisis.
Many Lebanese are furious at the failure to prevent the explosion of over 2,000 tonnes of ammonium nitrate.
The material, which was being stored in a warehouse, had been seized from a ship six years ago but never moved.
The government has promised to find those responsible.
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