Last week's blast at a warehouse storing highly explosive material killed at least 171 people, injured some 6,000 and damaged swathes of the Mediterranean city, compounding a deep economic and financial crisis.

"It is impossible that things go on as before," Foreign Minister Heiko Maas said. "The international community is ready to invest but needs securities for these investments. It is important to have a government that fights the corruption."

"Many in Europe have a lot of interest for this country. They want to know that there are economic reforms and good governance."

The resignation of Prime Minister Hassan Diab's government has deepened uncertainty. His cabinet's talks with the International Monetary Fund for a bailout had already stalled over internal differences about the scale of financial losses.

The foreign ministers of Russia and Saudi Arabia agreed on Wednesday on the importance of creating "beneficial external conditions" for the formation of a new Lebanese government, the Russian foreign ministry said.

Humanitarian aid has poured in but foreign countries have made clear they will not provide funds to help pull Lebanon from economic collapse without action on long-demanded reforms.

Aoun has promised a swift investigation into the blast at a warehouse where more than 2,000 tonnes of ammonium nitrate was stored for years without safety measures.

The president and prime minister were warned in July about the warehoused ammonium nitrate, according to documents and senior security sources.

The presidency said on Wednesday that as soon as Aoun received a state security report on the ammonium nitrate on July 20, the president's military consultant instructed the secretary general of the Supreme Defence Council to "do the necessary".

He later tweeted estimated losses from the blast exceed $15 billion, a bill Lebanon cannot pay given its financial crisis.

A donor conference raised pledges of nearly 253 million euros ($A416 million) for immediate relief. Maas gave a cheque for more than 1 million euro ($A1.6 million) to the Lebanese Red Cross, part of 20 million euros ($A33 million) in humanitarian aid from Germany.

The central bank has instructed local banks to extend interest-free dollar loans to individuals and businesses for essential repairs, and that it would in turn provide those financial institutions with the funding.

Volunteers and construction workers with bulldozers were still clearing wreckage from neighbourhoods more than a week after the blast. Rows of destroyed cars were still parked in front of damaged stores and demolished buildings.

Sitting amid the debris, Lebanese citizens said the state had abandoned them.

"Who knows what will happen. How will we get back to business," said Antoinne Matta, 74, whose safe and lock store was heavily damaged by the blast. Five employees were wounded.

Nagy Massoud, 70, was sitting on the balcony when the blast gutted his apartment. His pension is frozen in a bank account he cannot access due to controls prompted by the economic crisis.

"Where is the government," he said, looking around his shattered apartment.

Australian Associated Press