The blast left the entire city shaken.

The blast, which had began with a fire at the port, soon exploded into a mushroom of cloud as video footage of the incident went viral on the internet.

President Michel Aoun said 2,750 tonnes of ammonium nitrate had been stored unsafely in a warehouse for six years, reports BBC.

According to reports, the leader also announced that the government would release 100 billion lira (£50.5m; $66m) of emergency funds.

The country is observing an official three-day mourning from Wednesday.

Several people were trapped under rubble following the blast.

Cars were seen destroyed and left abandoned in the streets.

Several shops in the vicinity were reportedly damaged with window panes shattering on roads.

Rescue operation is still going on as rescuers are searching under rubble to find if people trapped under it.

The death toll is expected to rise.

Officials said on Tuesday that an investigation was under way to find the exact trigger for the explosion, BBC reported.

The ammonium nitrate had reportedly been unloaded from a ship impounded at the port in 2013, and then stored in a warehouse there, reports the British media.

Worst time in country:

This comes at a time when Lebanon is already gripped with tension ahead of the verdict in a trial over the killing of ex-PM Rafik Hariri in 2005.

A UN tribunal is due to announce its verdict in the murder case of Hariri on Friday.

Four alleged members of the Shiite Muslim movement Hezbollah are on trial in connection with the murder of Hariri in a car bomb attack.

Lebanon's economy is also suffering its worst economic crisis in decades, which has left nearly half of the population in poverty.

Countries offer help:

Fully equipped field hospitals from Qatar and Iraq to assist victims of the Beirut port blast will arrive in Lebanon on Wednesday, Lebanon's National News Agency reported.

It said two field hospitals, each designed for 500 beds, will be sent to Lebanon by Qatar, reports Sputnik news agency.

Another hospital will be sent by the Iraqi authorities. Baghdad also pledged to send fuel to Lebanon.

The authorities of Kuwait also promised to send medical aid to Lebanon. 

According to Sputnik, Turkish President Recep Tayyip Erdogan, during a telephone conversation with his Lebanese counterpart Michel Aoun, expressed his readiness to provide humanitarian assistance, including in the healthcare sector, in connection with the explosion in Beirut, the Turkish leader's administration said.

"Our president had a telephone conversation with Lebanese President Michel Aoun and wished Allah's mercy to those who died in the explosion that took place in Beirut today and the healing of the wounded," the administration said in a statement.

"According to him, Turkey is with the Lebanese people. The president noted that Turkey was ready for comprehensive humanitarian support, especiallyin the sphere of healthcare," it said. 

Donald Trump reacts:

US President Donald Trump said during a press conference that the massive explosion in the port of Beirut earlier on Tuesday was a "terrible attack."
"It looks like a terrible attack," Trump told reporters on Tuesday evening.

Trump also said that the United States stands ready to assist Lebanon in the aftermath of the deadly blast, reports Sputnik news agency.

Syrian President Bashar Assad offered condolences to his Lebanese counterpart, Michel Aoun, as well as to Lebanese people over a major explosion that hit Beirut on Tuesday.

"We are deeply upset by those events that took place at the Beirut port and resulted in a huge number of deaths and injuries. On behalf of the Syrian nation, we extend our sincere condolences to the Lebanese people, begging God for mercy for victims and the speedy recovery for all injured," Assad said in a telegram to Aoun, as quoted by the president’s office. 

WHO sending medical supplies:

The World Health Organization (WHO) is sending medical supplies to Lebanon for 500 wounded people as well as 500 surgery kits after a massive explosion took place in Beirut, WHO spokesperson Inas Hamam told Sputnik.

"Based on a request from the minister of health immediately after the blast, WHO is dispatching trauma kits containing emergency medical supplies enough to treat 500 injured people and surgical kits containing supplies to treat 500 people requiring surgical care," Hamam said on Tuesday. "Additional supplies will be dispatched as needed."

On Tuesday, a powerful explosion in the port of Beirut ripped through the center of the city and caused extensive damage, including to the Rafic Hariri International Airport located over six miles away from the epicenter of the blast.

“WHO is in constant contact with the local authorities (both the minister of health and hospitals treating the wounded) to further clarify needs and ensure immediate support,” Hamam said.

According to the Lebanese health minister, Hamad Hassan, the blast has claimed the lives of 63 people and more than 3,000 have been injured.“Our hearts and prayers are with all those affected, and we continue our mission to ensure the wellbeing of all people in Lebanon and across the region,” Hamam said.

WHO has also urged unity in the region amid the tragedy.

Even before the blast, Lebanon was facing civil unrest, economic hardship, coronavirus outbreak, and the Syrian refugee crisis,” Hamam said. “We call for regional solidarity to support all people in need in Lebanon given the additional challenges now faced.”