French President Emmanuel Macron announced on Wednesday that he would travel to Lebanon on Thursday, just two days after a massive explosion rocked the nation's capital, Beirut.

"I will go to Beirut tomorrow to meet the Lebanese people to bring them the message of fraternity and solidarity of the French. We will take stock of the situation with the political authorities," President Macron wrote on Twitter.

Various nations have moved swiftly to provide humanitarian aid to Lebanon in the wake of the blast which left at least 100 people dead and injured over 4,000.

Chinese President Xi Jinping earlier sent a message of condolence to his Lebanese counterpart Michel Aoun following the Tuesday blast.

In his message, Xi said he was shocked to learn about the huge explosions in Beirut, which caused heavy casualties.

On behalf of the Chinese government and people and in his own name, Xi extended profound condolences to the victims, conveyed heartfelt sympathies to the bereaved families and the injured, and wished the injured a quick recovery.

Other nations that have sent messages of condolence to Lebanon and offered their support include Israel, Armenia and Russia.

The cause of the blast is being investigated. But Lebanon's prime minister, Hassan Diab, said the cause of the explosion was 2,700 tonnes of ammonium nitrate stored in a warehouse for six years. President Michel Aoun tweeted it was "unacceptable" the explosives had been stored unsafely. Aoun declared three days of mourning and called for a two-week state of emergency.