'Horror show': Massive explosion in Beirut kills dozens, wounds thousands in Lebanon's capital

A massive explosion rocked Beirut with the force of an earthquake, followed by a shock wave that blew out windows and caused widespread damage across the Lebanese capital. At least 60 people were killed and more than 3,000 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.

Though the cause of the explosion is yet to be officially determined, Abbas Ibrahim, chief of Lebanese General Security, said it might have been caused by highly explosive material that was stored at the port after it was confiscated from a ship.

In a tweet on the Lebanese presidential account, the material was identified as ammonium nitrate, citing Prime Minister Hassan Diab as saying, "It is unacceptable that a shipment of ammonium nitrate estimated at 2,750 tons has been present for six years in a warehouse without taking preventive measures that endanger the safety of citizens."

. Ammonium nitrate, used in chemical fertilizer production, was a component of the bombing of the Oklahoma City federal building in 1995.

Videos showed an orange cloud over Beirut's port after the explosion, which is consistent with a nitrate-related explosion.

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.

Israel, which has seen years of intermittent conflict with Lebanon, particularly and recently with Hezbollah, denied any involvement and offered humanitarian medical aid. France and the United Nations special coordinator also offered humanitarian assistance.

"Our prayers go out to all the victims and their families. The U.S. stands ready to assist Lebanon. We have very good relations with the people of Lebanon and we will be there to help."

He added that "it looks like a terrible attack," even though no authorities have stated that it was an attack.

Online videos showed a dark pall rising from the port, what normally might be expected from an industrial-area fire. It was followed by an explosion creating a massive white cloud that enveloped the area. A moment later, the shock wave hit.

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, equivalent 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.

History: Even before explosion, Lebanon teetered toward collapse

“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.

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."