An Australian has been killed in a massive explosion in Beirut where at least 78 people have died and more than 4000 are injured.

Prime Minister Scott Morrison said Australia’s 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 on Wednesday.

Mr Morrison said there were normally about 20,000 Australians in the Lebanese capital.

But he’s unsure how many have 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.”

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.

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The blast damaged homes up to 10 kilometres away and left a trail of destruction throughout the city, with hospitals overwhelmed as emergency crews scrambled to help the thousands of people wounded.

Prime Minister Hassan Diab has declared a national day of mourning and the Lebanese Red Cross said “hundreds of casualties” were expected.

By 9.00am Wednesday (Australian time) Lebanese media was reporting at least 78 people had been confirmed dead. That number was expected to climb.

Videos posted to social media show a huge mushroom cloud forming above the city’s port district.

Witnesses have described how the boom was so loud it was deafening, leaving them with temporary hearing loss.

“At first, the building started to shake – I thought it was an earthquake,” said Ms Wahid, who works with Save the Children.

“Five of my nieces and nephews were out on the balcony playing when the blast went off.

“They started to scream and run as the windows collapsed around them; they were all wounded. Hospitals told us they couldn’t take them in because they were prioritising serious injuries.”

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The blast which could be felt in Cyprus, 250 kilometres away from the site of the explosion, raised suspicions it might have resulted from a rocket strike or detonation of explosives.

But the government clarified that it was believed to have started in a warehouse holding chemicals.

https://twitter.com/Alawaayy/status/1290726324810715137

Lebanon’s prime minister suggested the warehouse had been the subject of warnings going back to 2014.

The Guardian reports the PM indicated he would “reveal facts” about the warehouse soon, but had said did not want to pre-empt an investigation.

Eyewitness Bachar Ghattas told CNN it was “like an apocalypse”.

“You can see injured people all over the streets in Beirut, glass all over the place, cars are damaged,” Mr Ghattas said.

“It is very, very frightening what is happening right now and people are freaking out. The emergency services are overwhelmed.

“Beirut port is totally destroyed.”

Major General Abbas Ibrahim, of Lebanon’s General Security Directorate, said the blast was caused by confiscated “high explosive materials”.

It would be “naive to describe such an explosion as due to fireworks,” Mr Ibrahim told Lebanese TV.