Beirut explosion rocks Lebanon's capital city

What you need to know

• At least 137 people were killed and 5,000 wounded in a massive explosion that shook Beirut on Tuesday, according to Lebanon's health minister.

• Hundreds have been reported missing, raising fears that the death toll will rise, the health minister said Wednesday. 

• More than 300,000 people have been displaced from their homes. Authorities declared Beirut a "disaster city" and imposed a two-week state of emergency.

• It's still unclear what exactly caused the explosion. 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.