An Australian has been killed in a massive explosion in Beirut where at least 73 people have died and thousands more injured.
Prime Minister Scott Morrison said the Australian embassy in the Lebanese capital had been "significantly impacted" but staff escaped without major injuries.
"It's my deep regret to inform you that one Australian has been killed in this horrific blast," he told the Nine Network.
Mr Morrison said there were usually about 20,000 Australians in the Lebanese capital but he was unsure how many had returned to Australia because of the coronavirus pandemic.
"Our hearts really go out to our Lebanese Australian community," the prime minister said.
"I know there will be many prayers in the churches and the mosques in Australia but given the COVID restrictions, I would just urge the appropriate response."
Embassy damage
Foreign Minister Marise Payne said the embassy had considerable damage from the blast.
"About 95 per cent of the windows and front of the chancery of the embassy have been blown out," she told ABC radio.
"Staff have been affected by a number of glass injuries. Fortunately, they are relatively minor and they have all been treated."
Senator Payne said consular assistance had been extended to the family of the Australian who died.
Lebanese hospitals have been overwhelmed by victims from the blast and coronavirus.
"The challenge for many international supporters will be the context of COVID and how we work through that is something I'll be discussing with officials," Senator Payne said.
'Huge catastrophe'
The huge explosion ripped through a port warehouse district near the centre of Beirut and sent shockwaves across the Lebanese capital on Tuesday, shattering windows and causing apartment balconies to collapse.
At least 73 people were killed in the blast and over 3,700 others were injured, but officials expected the death toll to rise sharply as emergency workers dug through rubble across a swathe of the city to rescue people and remove the dead.
It was the most powerful blast to hit Beirut in years, making the ground tremble.
“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 - in all the streets and areas near and far from the explosion.”
Three hours after the blast, which struck shortly after 6pm, 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 being taken for treatment outside the city because Beirut hospitals were already packed with wounded.
Red Cross ambulances from the north and south of the country and the Bekaa valley to the east were called in to cope with the huge casualty toll.
About 2,750 tonnes of ammonium nitrate were stored in the Beirut port warehouse that exploded on Tuesday, Prime Minister Hassan Diab said.
Ammonium nitrate
"It is unacceptable that a shipment of 2,750 tonnes of ammonium nitrate has been present for six years in a warehouse, without taking preventive measures," he said at a defence council meeting, a spokesman told a press conference.
"It is unacceptable and we cannot remain silent on this issue."
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.

People injured in the Beirut Port explosion receive first aid at Najjar Hospital in Al-Hamra area in Beirut, Lebanon. Source: EPA
'Terrible attack'
President Donald Trump said Tuesday that US generals had told him that the powerful explosions which rocked Beirut appeared to have been caused by a "bomb of some kind."
"It looks like a terrible attack," Mr Trump told reporters at the White House.
"It would seem like it, based on the explosion," Mr Trump said. "I met with our generals and they feel that it was.
"This was not some kind of a manufacturing explosion type of event," he said.
"It seems to be, according to them - they would know better than I would - but they seem to think it was an attack.
"It was a bomb of some kind."
Footage of the explosion shared by residents on social media showed a column of smoke rising from the port district followed by an enormous blast, sending a ball of white smoke and fireball into the sky.
Those filming the incident from high buildings 2km from the port were thrown backwards by the shock.
Lebanon’s health minister said more than 25 people had been killed and more than 2,500 were injured.
Lebanon’s Red Cross said hundreds of people had been taken to hospitals.

Lebanese port workers walk at the explosion scene that hit the seaport of Beirut, Lebanon, Tuesday, 4 August, 2020. Source: AAP
Day of mourning
Lebanese President Michel Aoun called for an emergency meeting of the country’s Supreme Defence Council, according to the presidency’s Twitter account.
Prime Minister Hassan Diab called for a day of mourning on Wednesday and said that those responsible for the explosion would pay the price.
“I promise you that this catastrophe will not pass without accountability. ... Those responsible will pay the price,” he said in a televised speech.

People injured in the Beirut Port explosion receive first aid at Najjar Hospital in Al-Hamra area in Beirut, Lebanon. Source: EPA
“Facts about this dangerous warehouse that has been there since 2014 will be announced and I will not preempt the investigations”.
The explosion occurred three days before a UN-backed court is due to deliver a verdict in the trial of four suspects from the Shi’ite group Hezbollah over a 2005 bombing which killed former Prime Minister Rafik al-Hariri and 21 other people.
Mr Hariri was killed in another huge blast on the waterfront, although on that occasion it was caused by a truck bomb.

Destroyed vehicles following an explosion at the Beirut Port, Lebanon. Source: DAR AL MUSSAWIR
It was not immediately clear what caused Tuesday’s blaze that set off the blast.
Internal Security Chief Abbas Ibrahim, touring the port area, said he would not pre-empt investigations.
An Israeli official said Israel, which has fought several wars with Lebanon, had nothing to do with the blast.
The governor of Beirut port told Sky News that a team of firefighters at the scene had “disappeared” after the explosion.
“I saw a fireball and smoke billowing over Beirut. People were screaming and running, bleeding. Balconies were blown off buildings. Glass in high-rise buildings shattered and fell to the street,” said a Reuters witness.
Residents said glass was broken in houses from Raouche, on the Mediterranean city’s western tip, to Rabieh 10 km east.

A view shows the damaged Cavalier Hotel in Al-Hamra area in Beirut after the port explosion. Source: EPA
In Cyprus, a Mediterranean island 180 km across the sea from Beirut, residents heard the blast bangs.
One resident in Nicosia said his house and window shutters shook.
“All the downtown area windows are smashed and there are wounded people walking around. It is total chaos,” a Reuters witness said.