The blast, which shook the whole city, killed at least 113 people and injured more than 4,000 others. A two-week state of emergency has been declared.

President Michel Aoun said the blast was caused by 2,750 tonnes of ammonium nitrate stored unsafely in a warehouse.

All port officials have been put under house arrest pending an investigation.

Customs chief Badri Daher told local media that his agency had repeatedly called for the ammonium nitrate to be removed, but "this did not happen, and we leave it to the experts to determine the reasons".

Ammonium nitrate is used as a fertilizer in agriculture and as an explosive.

Opening an emergency cabinet meeting, President Aoun said: "No words can describe the horror that has hit Beirut last night, turning it into a disaster-stricken city".

The explosion occurred just after 18:00 (15:00 GMT) after a fire at the port, and it was felt 240 km (150 miles) away on the island of Cyprus, in the eastern Mediterranean.

Security forces have sealed off a wide area around the blast site, and rescuers have been looking for bodies and survivors under rubble while boats searched the waters off the coast.

Public Health Minister Hamad Hassan said a "large number of children" had been rescued but added that he feared that the number of dead would rise further.