At least 73 people died and about 3,700 were injured Tuesday after a massive explosion in downtown Beirut that shattered windows and caused apartment balconies to collapse, Lebanese Health Minister Hamad Hassan said.

While the cause of the explosion was not immediately known, local media citing the country's authorities said that ammonium nitrate stored in the port may have triggered the blast.

Men stand before wrecked buildings after a massive explosion near Beirut, Lebanon on Aug. 4, 2020.(Getty/Kyodo)

Related coverage:

Rusted gas pipe likely behind deadly explosion in northeastern Japan

1 dead, 18 hurt in Fukushima explosion, gas leak suspected

The explosion is the biggest in Beirut in years, Reuters said, quoting the country's president, Michel Aoun, as saying 2,750 tons of ammonium nitrate had been stored for six years at the port without safety measures.

In Washington, President Donald Trump said senior U.S. military officials seem to think the blast was an "attack" rather than "some kind of a manufacturing explosion type of event."

"It was a bomb of some kind," Trump told a press conference, without elaborating, while noting that the United States "stands ready to assist Lebanon."

According to the Japanese Embassy in Lebanon, one Japanese sustained minor injuries due to shattered glass.

Australian Prime Minister Scott Morrison tweeted Wednesday that he has confirmed the death of one Australian in the blast.

Hospitals in the Lebanese capital were overwhelmed as injured people were brought in, according to local media.

The blast, which sent up "a huge mushroom cloud-like shockwave," resulted in damage to buildings across a radius of several kilometers, CNN said.

After the explosion, Israel said it had no involvement with the incident, local media reported. Israel and Hezbollah, a Shia militant group in Lebanon, were involved in a month-long conflict in 2006.