A massive explosion rocked Beirut, Lebanon, with the force of an earthquake followed by a shock wave that caused widespread damage across the capital.
At least 50 people were killed and more than 2,700 wounded, according to Health Minister Hassan Hamad.
The blast followed a fire that broke out in the city's port area, based on multiple videos from the scene.
While the cause of the explosion was yet to be officially determined, Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was confiscated from a ship that was being stored at the port. Local television channel LBC said the material was sodium nitrate.
Israel, which has seen years of intermittent conflict with Lebanon, quickly denied any involvement. An Israeli government official, speaking on condition of anonymity because he was not authorized to discuss the matter with the media, told the Associated Press that Israel “had nothing to do” with the blast.
The force shook buildings, which were hit again by the shock wave that blew out windows, sending shards of glass flying.
Beirut Gov. Marwan Abboud called it a "national catastrophe," and the prime minister declared a day of mourning, according to CNN.
“It resembles 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 of the mushroom cloud.
The White House and U.S. State Department said they are monitoring the situation.
"Having witnessed the horrific explosions at the port this evening, our heartfelt sympathies go out to the victims and their families. We mourn each loss from this terrible tragedy alongside the Lebanese people," U.S. Ambassador Dorothy Shea said.
Online videos showed a dark pall rising from the port, what normally might be expected from an industrial-area fire. It is followed by an explosion creating a massive white cloud that envelops the area. A moment later, the shock wave hits.
The blast, which occurred shortly after 6 p.m. local time, was followed by the wail of ambulance sirens through streets covered in debris.
The Beirut explosion recalled the twin blasts that killed at least 50 and injured more than 700 in the Chinese port of Tianjin in 2015. The second was the more powerful of the two, equivilent to an estimated 21 tons of TNT.
Over the past few decades, Beirut has endured bloodshed from suicide bombings, armed conflict with neighboring Israel and a civil war.
“It was a real horror show. I haven’t seen anything like that since the days of the (civil) war,” said Marwan Ramadan, who was knocked off his feet by the explosion.
History: Even before explosion, Lebanon teetered toward collapse
CNN's Beirut correspondent Ben Wedeman said he "never felt anything like it ... [I've] been around the block and seen pretty large explosions ... and this was bigger."
Washington Post Beirut bureau chief Liz Sly reported "bleeding people, wreckage piled all over."
Contributing: The Associated Press