Rescue workers in Lebanon are searching for more than a hundred people who are missing after a huge explosion devastated the port area of the capital Beirut on Tuesday, the BBC reports.

The blast killed at least 100 people and injured more than 4,000 others.

The whole city was shaken by the explosion and a mushroom cloud could be seen spreading over the port area.

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

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

He scheduled an urgent cabinet meeting for Wednesday, and said a two-week state of emergency should be declared.

The country will observe an official period of mourning for three days from Wednesday.

Eyewitness Hadi Nasrallah says that he saw the fire but did not expect the blast. "I lost my hearing for a few seconds, I knew something was wrong, and then suddenly the glass just shattered all over the car, the cars around us, the shops, the stores, the buildings. Just glass going down from all over the building," he told the BBC.

BBC Arabic reporter Maryem Taoumi was conducting a video interview in Beirut with a member of the Moroccan Agency for Sustainable Energy at the time of the explosion.-Graphic: BBC

Lebanese soldiers search for survivors after a massive explosion in Beirut, Lebanon, Wednesday.

Rescuers search for 100 missing in Lebanon