One Australian was among 135 people killed in the explosion at Beirut port, which injured more than 5000 and left up to 250,000 with homes.

Lebanese rescue workers began digging through the rubble searching for survivors.

The explosion was the most powerful ever to hit Beirut, a city still scarred by civil war three decades ago and reeling from an economic meltdown and a surge in COVID-19 infections.

It sent a mushroom cloud into the sky and rattled windows on the Mediterranean island of Cyprus, about 160km away.

Lebanon's President, Michel Aoun, said 2750 tonnes of ammonium nitrate, used in fertilisers and bombs, had been stored for six years at the port without safety measures. He called it "unacceptable".

He told the nation the government was "determined to investigate and expose what happened as soon as possible, to hold the responsible and the negligent accountable, and to sanction them with the most severe punishment."

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Foreign Affairs Minister Marise Payne said Australia would give $1 million each to the World Food Program and Red Cross.

The funding would be drawn from the aid budget.

Senator Payne said the Australian embassy in Beirut had been significantly damaged but all staff were safe.

Australians in Lebanon in need of assistance should contact the Department of Foreign Affairs and Trade on +61 2 6261 3305 and monitor smartraveller.com.au.

Those in Australia who are concerned about friends and family in Lebanon should call 1300 555 135.

- with AAP