Beirut's governor Marwan Abboud called it a "national catastrophe" and the prime minister declared a day of mourning, according to CNN.
“It resembles to what happened in Japan, in Hiroshima and Nagasaki. That’s what [it] reminds me of. In my life, I haven’t seen destruction on this scale," Abboud said.
The White House and U.S. State Department said they are monitoring the situation.
The cause of the blast was not immediately clear. It came at a time when Lebanon is passing through its worst economic and financial crisis in decades.
Online video showed a column of smoke rising from the port area from what appeared to be an initial explosion, followed by a massive blast that sent up a mushroom cloud and a sho＊ wave racing over the city.