BEIRUT (REUTERS, BLOOMBERG) - Lebanon's Cabinet on Wednesday (Aug 5) declared a two-week state of emergency in Beirut, following a massive explosion in the port that rocked the city on Tuesday, and handed control of security in the capital to the military.

The Cabinet instructed the military to impose house arrest on anyone involved since 2014 in the administration of the warehouse containing vast amounts of highly-explosive material that blew up, according to a statement read out by the information minister.

It also approved an exceptional allocation of 100 billion Lebanese pounds (S$91 million) to deal with the crisis.

The volatile chemical suspected of causing the deadly explosion that flattened Lebanon's main port had been lying in storage there for six years, despite warnings from customs officials about its hazards, documents show.

The ammonium nitrate - equivalent to 1,800 tons of TNT - was unloaded from the cargo ship Rhosus in 2014, according to two letters issued by the director general of Lebanese Customs.

For reasons that are unclear, dockworkers unloaded the chemical, which can be used to make fertilisers and explosives, and put it into storage.

Workers welding a door on Tuesday started a fire that ignited the chemicals, Lebanese broadcaster LBCI said, citing people who attended a Supreme Council of Defence briefing after the blast.

The authorities have not said what triggered the explosion that roared through Beirut, killing at least 100 people and wounding 4,000.

Customs officials asked judicial authorities at least twice to issue orders for the highly inflammable substance to be confiscated or re-exported, according to the letters from the customs authority.

In one of the letters, dated May 3, 2016, the director general at that time, Shafik Merhe, warned of "the extreme danger" from storing the chemical in a warehouse "in these unsuitable weather conditions", saying it posed a risk to the staff and port.

LBCI reported on Wednesday that the Rhosus had been scheduled to sail with its cargo from Beirut six years ago, but stayed at the port due to a mechanical failure.

Prime Minister Hassan Diab on Tuesday described the storage of 2,750 tons of ammonium nitrate at the port as "unacceptable" and vowed those responsible would be held accountable.

The widely used commercial chemical explosive is almost as powerful as dynamite.

In 1995, Timothy McVeigh used about 2 tons of it to blow up the Alfred P. Murrah Federal Building in Oklahoma, killing 168 people.

As Lebanese army personnel and rescue workers sifted through the rubble, looking for dozens of missing people, the government placed all port officials under house arrest, Information Minister Manal Abdel-Samad told reporters after an emergency Cabinet meeting.

As the two-week state of emergency has been imposed in the city, a coronavirus-related lockdown was extended for the next two months.

Outrage over the government's role in the calamity ran high in a country already groaning under the weight of its worst financial crisis and a resurgent coronavirus outbreak.

Dozens of people gathered in downtown Beirut as former Prime Minister Saad Hariri inspected the damage, beating cars in his convoy and shouting: "They killed Beirut".

The explosion was so powerful that it was heard in Cyprus, and severely damaged buildings kilometres away.

Massive shipping containers were flipped upside down as if they were toys, and cranes melted under the intense fire that still burned on Wednesday, and was being doused by helicopters whirring above.

"It's like an apocalypse," lawmaker Yassine Jaber told Bloomberg. "Pure negligence and that's the ultimate manifestation of how bad governance has been in Lebanon, with no accountability whatsoever, a manifestation of failure that should jolt us to wake up."

Hospitals, already stretched to capacity by the virus emergency, were overwhelmed.

The government appealed to other countries for emergency aid as concerns mounted over food supply in the import-dependent nation.

Wheat silos at the port were damaged, and their contents - equal to about six weeks of the country's needs - were rendered unfit for consumption, Economy Minister Raoul Nehme said. He assured Lebanese there would be no flour or bread crisis.

France and various Arab states pledged medical aid, while Germany offered members of its armed forces to aid search operations. French President Emmanuel Macron plans to visit Lebanon on Thursday, Agence France Presse reported.

"The damage is massive at the port and it will take a very long time to fix and build," Public Works Minister Michel Najjar told a local television station. The port at Lebanon's second-largest city, Tripoli, will serve as the alternative, possibly backed up by facilities in Sidon and Tyre, Najjar said.

The Beirut port handles 6 million tons of shipments a year.

Before the blast, talks with the International Monetary Fund for a US$10 billion (S$14 billion) loan had stalled over the government's failure to agree on a reform plan, and Gulf states deflected Lebanon's request for a bailout, afraid money would fall into the hands of Iran-backed Hezbollah militants. Officials had been discussing ways to partially privatise the port.