People in Beirut have expressed anger at the government over what they say was negligence that led to Tuesday's huge explosion.
President Michel Aoun said the blast was caused by 2,750 tonnes of ammonium nitrate stored unsafely in a warehouse.
Many have accused the authorities of corruption, neglect and mismanagement.
The blast killed at least 137 people and injured about 5,000 others, while dozens are still missing. A two-week state of emergency has begun.
French architect Jean-Marc Bonfils, involved in rebuilding the city after the civil war, and firefighter Sahar Fares, one of the first responders at the scene, were among the first fatalities to be named. A German diplomat was also among the dead.
French President Emmanuel Macron - the first world leader to visit since the tragedy - was mobbed as he walked through the city on Thursday, with residents imploring him to help and denouncing their leaders.
"Help us, you are our only hope," one resident called out. "Please don't give money to our corrupt government," said another, before adding: "We can't take this any more."
At a press conference, Mr Macron said a new political order was needed in Lebanon. "The anger I saw in Beirut today also showed signs of hope for the future," he said.
He said France would help organise international aid to Lebanon. Funding was available, he said, but political reforms had to take place before it could be sent.
He vowed that there would be no blank cheques for Lebanon's leaders, but cautioned that he could not tell the Lebanese government what to do. France is the former colonial power in Lebanon.
Filmmaker Jude Chehab told the BBC: "Beirut is crying, Beirut is screaming, people are hysterical and people are tired."
Chadia Elmeouchi Noun, a resident currently in hospital, said: "I've known all the time that we are led by incompetent people, incompetent government... But I tell you something - what they have done now is absolutely criminal."
On Wednesday, the government announced that a number of port officials were placed under house arrest pending an investigation into the explosion.
The country's Supreme Defence Council insisted that those found responsible would face the "maximum punishment".
Meanwhile, Amnesty International and Human Rights Watch (HRW) have called for an independent investigation into the blast. In a statement, HRW said it had "serious concerns about the ability of the Lebanese judiciary to conduct a credible and transparent investigation on its own".
A city of sirens, empty buildings and empty streets
By Quentin Sommerville, BBC News, Beirut
This port was Lebanon's lifeline to the whole world. Something like 80% of the county's grain came through here. I can see the grain silos, which were built way back when, and they're teetering really. They no longer look like they're going to survive. Just beyond there I can see a ship listing heavily. I've lived in Beirut for five years and it's almost unrecognisable - it's a city of sirens, of empty buildings, of empty streets.
As I look at the neighbourhood of Gemmayze just behind the port, I don't think I can see a single pane of glass left. Entire roofs have gone - I can see friends' apartments which are just open to the sky now. All of this area, which was really heavily populated, has been abandoned. No one is coming back here anytime soon.
What's really noticeable as you walk the streets here is that every second person seems to have a broom in their hand. There are clear-up teams everywhere, but it's pretty low tech: tiny teams of people with pans and brushes to clean up an an entire city's devastation.
The thing that really strikes me is how enormously stupid it was, what criminal negligence it took to leave this highly explosive material right in the very heart of this city, within yards of people, their homes, their businesses. And the authorities here knew - they had been warned that these chemicals were dangerous and that they were a great risk to Beirut and Lebanon.
What triggered the explosion?
The ammonium nitrate - which is used as a fertiliser and as an explosive - had been in a warehouse in the port for six years after it was unloaded from a ship impounded in 2013.
The head of the port and the head of the customs authority said that they had written to the judiciary several times asking that the chemical be exported or sold on to ensure port safety.
Port General Manager Hassan Koraytem told OTV they had been aware that the material was dangerous when a court first ordered it stored in the warehouse, "but not to this degree".
House arrest would apply for all port officials "who have handled the affairs of storing [the] ammonium nitrate, guarding it and handling its paperwork" since June 2014, said Information Minister Manal Abdel Samad.
The ammonium nitrate arrived on a Moldovan-flagged ship, the Rhosus, which entered Beirut port after suffering technical problems during its voyage from Georgia to Mozambique, according to Shiparrested.com, which deals with shipping-related legal cases.
The Rhosus was inspected, banned from leaving and was shortly afterwards abandoned by its owners, sparking several legal claims. Its cargo was stored in a port warehouse for safety reasons, the report said.
More on the explosion in Beirut
What is the latest on rescue efforts?
A French rescue team working in the city said there was still a good chance of finding survivors, two days after the explosion.
One unnamed rescuer told Mr Macron that they hoped to find a group of seven or eight people believed to be trapped in a "control room" under the rubble.
Security forces have sealed off a wide area around the blast site.
Flights carrying medical aid, rescuers and mobile clinics have been arriving from France and other countries since Wednesday. The UK is sending up to £5m ($6.6m) in medical aid, Foreign Secretary Dominic Raab said.
Public Health Minister Hamad Hassan said Lebanon's health sector was short of beds and lacked the equipment necessary to treat the injured and care for patients in critical condition.
As many as 300,000 people have been left homeless by the blast, said Beirut's governor Marwan Aboud.
He told the BBC: "Beirut needs food, Beirut needs clothes, houses, materials to rebuild houses. Beirut needs a place for the refugees, for its people."
Economy Minister Raoul Nehme meanwhile said the country would have to rely at least partly on foreign aid to rebuild.
"We're not swimming in dollars," he told Sky News Arabia.
What's the background?
The explosion comes at a sensitive time for Lebanon. With Covid-19 infections on the rise, hospitals were already struggling to cope. Now, they are faced with treating thousands of injured people.
The country is also going through the worst economic crisis since the 1975-1990 civil war, and tensions were already high with street demonstrations against the government. People have to deal with daily power cuts, a lack of safe drinking water and limited public healthcare.
Lebanon imports most of its food and large quantities of grain stored in the port have been destroyed causing fears of widespread food insecurity to come. The future of the port itself is in doubt.
The government says it will release 100bn lira (£50.5m; $66m) of emergency funds but the impact of the blast on the economy is expected to be long-lasting.
The explosion happened close to the scene of a huge car bombing which killed former Prime Minister Rafik Hariri in 2005. A verdict in the trial of four men accused of orchestrating the attack was due on Friday at a special court in the Netherlands, but this has been postponed until 18 August out of respect for the victims of Tuesday's blast.
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