Officials said they expected the death toll to rise further after the blast as emergency workers dug through rubble to rescue people and remove the dead. It was the most powerful explosion in years to hit Beirut, which is already reeling from an economic crisis and a surge in coronavirus infections.
Prime Minister Scott Morrison said one Australian had been killed and Australia's embassy had been "impacted significantly" in the explosion. Foreign Minister Marise Payne said some embassy staff were hit by flying glass when the building's windows were blown out, ABC reported.
Lebanon's interior minister said initial information indicated highly explosive material, seized years ago, that had been stored at the port had blown up. Israel, which has fought several wars with Lebanon, denied any role and offered help.
"What we are witnessing is a huge catastrophe," the head of Lebanon's Red Cross George Kettani told broadcaster Mayadeen. "There are victims and casualties everywhere."
Hours after the blast, which struck shortly after 6pm local time, a fire still blazed in the port district, casting an orange glow across the night sky as helicopters hovered and ambulance sirens sounded across the capital.
A security source said victims were taken for treatment outside the city because Beirut hospitals were packed with wounded. Ambulances from the north and south of the country and the Bekaa valley to the east were called in to help.
The blast was so big that some residents in the city, where memories of heavy shelling during the 1975 to 1990 civil war live on, thought an earthquake had struck. Dazed, weeping and wounded people walked through streets searching for relatives.
"I promise you that this catastrophe will not pass without accountability," Prime Minister Hassan Diab told the nation.
"Those responsible will pay the price," he said in his televised address, adding that details about the "dangerous warehouse" would be made public.
The interior minister told Al Jadeed TV that ammonium nitrate had been stored at the port since 2014.
The US embassy in Beirut warned residents in the city about reports of toxic gases released by the blast, urging people to stay indoors and wear masks if available.