At least 100 people were killed and 4,000 wounded in a massive explosion that shook Beirut on Tuesday. It’s still unclear what exactly caused the explosion, centred on the Lebanese capital’s port. It was earlier blamed on a fire that broke out. Lebanon’s Prime Minister said an investigation would focus on an estimated 2,750 metric tons of the explosive ammonium nitrate stored at a warehouse.

Video footage of the blast shows an enormous bright red ball of fire shaking and shattering all the buildings around it. The explosion sent shockwaves through the city, leaving thousands destitute and hospitals overwhelmed with the aftermath.

Lebanese media have reported that the explosion was the worst crisis the country has seen since the 1975 civil war.