Lebanese rescue workers are digging through rubble looking for survivors after a massive warehouse explosion sent a devastating blast wave across Beirut, killing at least 100 people and injuring nearly 4000.
Prime Minister Scott Morrison confirmed on Wednesday morning one Australian citizen was among those killed by the explosion.
"We obviously can't confirm details of that at this stage because there is contacts with families and others," Mr Morrison told Nine's Today Show.
"But our hearts go out to all of those in Lebanon and in Beirut in particular at the moment. You can see from the image of the blast, it is just absolutely devastating."
He said all staff at the Australian embassy in Beirut were safe but the building had been "significantly compromised".
Officials said the toll was expected to rise after the blast at port warehouses that stored highly explosive ammonium nitrate, with reports fireworks were also stored in the area and may have caught fire and ignited the chemicals.
The explosion was the most powerful ever to rip through Beirut, a city still scarred by civil war three decades ago and reeling from an economic meltdown and a surge in coronavirus infections.
It sent a mushroom cloud into the sky and rattled windows on the Mediterranean island of Cyprus, about 160km away.
Foreign Minister Marise Payne said the government was prepared to assist the Lebanese government.
"The COVID-19 challenge of course complicates that as well, in terms of international movement," she said.
"Being conscious of that, we'll provide what support we can."
Senator Payne said it was a "very, very serious" industrial accident, not an attack, as US President Donald Trump had earlier claimed.
Lebanon's President, Michel Aoun, said 2750 tonnes of ammonium nitrate, used in fertilisers and bombs, had been stored for six years at the port without safety measures. He called it "unacceptable".
He told the nation the government was "determined to investigate and expose what happened as soon as possible, to hold the responsible and the negligent accountable, and to sanction them with the most severe punishment."
An official source familiar with preliminary investigations blamed the incident on negligence. Ordinary Lebanese directed anger at politicians who have overseen decades of state corruption and bad governance that plunged the nation into financial crisis.
Prime Minister Hassan Diab promised accountability for the blast at the "dangerous warehouse", adding "those responsible will pay the price".
The head of Lebanon's Red Cross, George Kettani, said at least 100 people had been killed. "We are still sweeping the area. There could still be victims. I hope not," he said.
Facades of central Beirut buildings were ripped off, furniture was sucked into streets and roads were strewn with glass and debris. Cars near the port were flipped over.
Senator Payne said 95 per cent of the embassy's windows had been blown out by the impact.
"A number of staff have received glass injuries. They are being supported and looked after. Thankfully none of those injuries is very serious. But, of course, it's a shocking and terrifying incident to be dealing with and I really send our thoughts to our teams who are on the ground in Beirut, including Ambassador Rebekah Grindlay," Senator Payne told 2GB.
Around 20,000 Australians are generally living in Beirut, Mr Morrision said, although it was not known how many returned to Australia due to the pandemic.
In a tweet, Mr Morrison said Australia "stands ready to provide our support, including to any Australians affected."
Senator Payne said she was "shocked and saddened" by the horrific event.
"Tragically, we have lost one Australian. We are not going into the details of that at the moment, while we work with family and consular authorities to support them. And we are very, very sorry about that and convey our sympathy to the family and friends of that Australian," Senator Payne said.
"But as you say ... the size of this event, the size of the explosion, and its impact, is going to have caused a very significant number of fatalities. So we will work closely with local authorities to establish the extent of the impact on Australians.
"We think there are usually around 20,000 Australians, including dual nationals in Lebanon, at any one time. That figure may have been impacted by movements related to COVID-19, but it's still a very considerable figure and our team has been working very hard to support them."
A phoneline has been set up for anyone in need of urgent help, on +61 2 6261 3305.
"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 local time on Tuesday, 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.
President Donald Trump said the US "stands ready to assist Lebanon," and US Secretary of State Mike Pompeo extended his "deepest condolences".
"Our team in Beirut has reported to me the extensive damage to a city and a people I hold dear, an additional challenge in a time of already deep crisis," Pompeo said in a written statement.
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.
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.
Lebanon's interior minister said initial information indicated highly explosive material, seized years ago, that had been stored at the port had blown up.
The minister later told al-Jadeed TV ammonium nitrate had been in storage there since 2014.
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.
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.
Officials did not say what caused the blaze that set off the blast. A security source and media said it was started by welding work being carried out on a hole in the warehouse.
Internal Security Chief Abbas Ibrahim, touring the port area, said he would not pre-empt investigations.
For many it was a dreadful reminder of the 1975 to 1990 civil war that ripped the nation apart and destroyed swathes of Beirut, much of which had been rebuilt. Post-war reconstruction and political corruption mired Lebanon in huge debts.
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.
In Cyprus, a Mediterranean island 180km across the sea from Beirut, residents heard the blast bangs.
One resident in Nicosia said his house and window shutters shook.
- with AAP
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