Two enormous explosions devastated Beirut's port on Tuesday, leaving at least 73 people dead and thousands injured, shaking distant buildings and spreading panic and chaos across the Lebanese capital.

The second blast sent an enormous orange fireball into the sky, flattened the harbourside and drove a tornado-like shockwave through the city, shattering windows kilometres (miles) away.

Bloodied and dazed wounded stumbled among the debris, glass shards and burning buildings in central Beirut as the health ministry reported 73 dead and 3,700 injured and the minister bemoaned "a disaster in every sense of the word".

A soldier at the port, where relatives of the missing scrambled for news of their loved ones, told AFP: "It's a catastrophe inside. There are corpses on the ground. Ambulances are still lifting the dead."

The blasts were heard throughout the small country and as far away as Nicosia on the eastern Mediterranean island of Cyprus, 240 kilometres (150 miles) away. 

"It was like an atomic bomb," said Makrouhie Yerganian, a retired schoolteacher in her mid-70s who has lived near the port for decades. 

"I've experienced everything, but nothing like this before," even during the country's 1975-1990 civil war, she said. "All the buildings around here have collapsed."

Her 91-year-old uncle, who lived in the same building, was wounded in the blast and later died.

The cause of the explosions was not immediately clear but a top official, General Security chief Abbas Ibrahim, said confiscated explosive materials had been stored at the city's port.

"It appears there is a warehouse containing material that was confiscated years ago, and it appears that it was highly explosive material," he said.

Lebanon's President Michel Aoun called an urgent meeting of the national defence council, which declared Beirut a disaster zone, while Prime Minister Hassan Diab declared Wednesday a day of mourning.

"What happened today will not pass without accountability," said Diab. "Those responsible for this catastrophe will pay the price."

An Israeli government official who requested anonymity told AFP: "Israel had nothing to do with the incident."

Benjamin Strick, who works with investigations website Bellingcat, said on Twitter that the explosions appeared to have been centred on a 130-metre (420 foot)-long grey warehouse alongside a dock. 

Retired US nuclear scientist Cheryl Rofer tweeted that the "red cloud" of the massive blast was "very likely ammonium nitrate", a common agricultural fertiliser that is a highly explosive compound.

'We saw the mushroom'

Diab appealed for international assistance for Lebanon, which is already mired in its worst economic crisis in decades.

"I am sending an urgent appeal to all countries that are friends and brothers and love Lebanon, to stand by its side and help us treat these deep wounds," the prime minister said. 

Condolences poured in from across the world with Gulf nations, the United States and even Lebanon's arch foe Israel offering to send aid.

AFP video footage showed areas of near-complete devastation, with cars flipped onto their roofs like children's toys, warehouses flattened and survivors drenched from head to toe in their own blood. 

Across Beirut, entire streets were wiped out, glass shards littered much of the inner city and the country's Red Cross called for urgent blood donations.

"We heard an explosion, then we saw the mushroom," said a Beirut resident who witnessed the second, deafening explosion from her balcony in the city's Mansourieh district. 

"The force of the blast threw us backwards into the apartment."

An AFP correspondent at the scene minutes after said every shop in the Hamra commercial district had sustained damage, with entire storefronts destroyed and many cars wrecked.

A huge blaze sent up black smoke from the port area, as helicopters dumped water on burning buildings. 

A ship moored off the port was on fire, and the blasts also damaged a ship deployed with United Nations peacekeeping force UNIFIL and injured some of its personnel.

'Like an earthquake' 

Hundreds immediately shared their shock and grief on social media.

"Buildings are shaking," tweeted one resident, while another wrote: "An enormous, deafening explosion just engulfed Beirut. Heard it from miles away."

Online footage from a Lebanese newspaper office showed blown out windows, scattered furniture and demolished interior panelling.

The explosions hit a country already reeling from its worst economic crisis in decades which has left nearly half of the population in poverty, as well as from the coronavirus pandemic.

Lebanon's economy has collapsed in recent months, with the local currency plummeting, businesses closing en masse and poverty soaring at the same alarming rate as unemployment. 

Charity Save the Children said "the incident could not have occurred at a worse time". 

The explosions came three days before a UN tribunal's verdict on the murder of former Lebanese premier Rafic Hariri, who was killed in a huge 2005 truck bomb attack. 

Four alleged members of the Shiite Muslim movement Hezbollah are on trial in absentia at the court in the Netherlands over the huge Beirut bombing that killed Sunni billionaire Hariri and 21 other people. 

A woman in the city centre Tuesday told AFP the blast "felt like an earthquake" and "bigger than the explosion in the assassination of Rafic Hariri in 2005".