Authorities say the tragedy may have been caused by a large amount of ammonium nitrate being stored in a warehouse.
Lebanon's prime minister has called for a day of mourning on Wednesday after a huge explosion killed at least 100 people and injured more than 4,000 in Beirut.
Hassan Diab called Tuesday afternoon's explosion a "big catastrophe" and said those responsible would pay the price.
He tweeted that the explosion was caused by more than 2,700 tonnes of ammonium nitrate left unsecured at a warehouse near the city's port for six years.
The head of Lebanon's Red Cross, George Kettaneh, said at least 100 people were killed and more than 4,000 were wounded, adding the toll could rise further.
Video shows the moment a building exploded, sending a huge shockwave across the city that was heard and felt as far away as Cyprus - more than 125 miles (200km) away.
Pictures showed cars upturned and streets covered in shattered glass and twisted metal.
Lebanon's internal security chief, Abbas Ibrahim, also said the blast may have been caused by explosive material confiscated from a ship and stored at the port.
Earlier reports had suggested the building was a fireworks storage warehouse.
US President Donald Trump said his generals believed the explosion was probably a bomb attack - but did not provide any evidence or further explanation.
Residents reported collapsed ceilings and shattered windows as far away as 2km (1.2 miles), as a huge column of red smoke rose over the city.
People were seen wounded on the ground near the port, according to a photographer at the scene.
One hospital said it could not take any more patients and was appealing for blood, local media said, as others pleaded for generators to keep their lights on.
Sky News Middle East editor Zein Ja'far, who was in downtown Beirut at the time of the explosion, said it had caused windows to "cave in".
Lebanon's prime minister has called for a day of mourning on Wednesday after a huge explosion killed at least 100 people and injured more than 4,000 in Beirut.
Hassan Diab called Tuesday afternoon's explosion a "big catastrophe" and said those responsible would pay the price.
He tweeted that the explosion was caused by more than 2,700 tonnes of ammonium nitrate left unsecured at a warehouse near the city's port for six years.
Video shows the moment a building exploded, sending a huge shockwave across the city that was heard and felt as far away as Cyprus - more than 125 miles (200km) away.
Pictures showed cars upturned and streets covered in shattered glass and twisted metal.
Lebanon's internal security chief, Abbas Ibrahim, also said the blast may have been caused by explosive material confiscated from a ship and stored at the port.
Earlier reports had suggested the building was a fireworks storage warehouse.
US President Donald Trump said his generals believed the explosion was probably a bomb attack - but did not provide any evidence or further explanation.
Residents reported collapsed ceilings and shattered windows as far away as 2km (1.2 miles), as a huge column of red smoke rose over the city.
One hospital said it could not take any more patients and was appealing for blood, local media said, as others pleaded for generators to keep their lights on.
Sky News Middle East editor Zein Ja'far, who was in downtown Beirut at the time of the explosion, said it had caused windows to "cave in".