Ammonium nitrate stored at site of massive Beirut explosion: Officials

LONDON -- More than 2,700 tons of ammonium nitrate was stored in the Beirut warehouse that was the scene of Tuesday's deadly explosion that killed dozens of people in the Lebanese capital, authorities say.

At least 70 people are dead and more than 3,500 injured following the massive explosion that rocked the city Tuesday evening, according to the Lebanese health minister. Footage from the ground showed significant damage and plumes of smoke rising above the city.

Two explosions occurred in Beirut's port, according to the Agence France-Presse. Firefighters were seen battling flames at a warehouse at the scene of the blast, officials said.

An estimated 2,750 tons of ammonium nitrate, an explosive compound, was stored in the warehouse, according to Lebanon Prime Minister Hassan Diab.

According to the office of Lebanese President Michel Aoun, Diab said that it is unacceptable that the compound was stored there for six years without precautionary safety measures in place.

Following a meeting with Lebanon's Supreme Defense Council, Diab said he will not be satisfied until someone is held accountable for the explosion.

After the meeting, Aoun declared Beirut a disaster zone and announced a two-week state of emergency. The military will have the authority to maintain security, Aoun said, according to a tweet from his office.

The Lebanese health minister originally said at least 50 people were killed and 2,700 were injured in the explosion, then raised the numbers to 70 dead and more than 3,500 injured.

The U.S. embassy in Beirut has issued a security alert warning Americans to "stay indoors and wear masks if available" because "there are reports of toxic gases released in the explosion."

The German Foreign Office said on social media that German embassy employees are among the injured.

The United States Geological Survey reports that the explosion registered a magnitude of 3.3. The blast itself was heard up to 25 miles south of the city, and many streets in Beirut are now paved with broken glass.

In an address to the nation, Diab said that the disaster will not pass "without accountability," and those responsible "will pay the price."

The "truth" about the six-year-old warehouse "will be revealed," he added.

Ghada Alsharif, a reporter from the Daily Star, one of Lebanon's most prominent news outlets, posted a video on social media showing significant damage within the newspaper's office building. Firefighters were seen battling flames at the scene of the blast.

The Lebanese Red Cross have dispatched 30 teams to the scene and are making an urgent call for blood donations.

Other eyewitnesses said there were multiple fires burning and that windows of apartment buildings were shattered in a large radius around the blast site. Video from the ground in Beirut shows cars crushed by rubble, injured people walking through debris and extensive damage to nearby buildings.

Hospitals in Beirut are so overwhelmed that some have been turning the injured away, with some of the injured now driving to Tripoli, 50 miles north, to receive treatment.

Alyssa Farah, the White House director of Strategic Communications, tweeted that President Donald Trump has been briefed on the explosion.

"Praying for the safety of the people of Lebanon," she posted on Twitter. "The President has been briefed. We continue to monitor the situation closely."

A U.S. State Department spokesperson said in a statement that the U.S. has "no information about the cause of the explosion." The department is working with local authorities to determine if any U.S. citizens were affected, the spokesperson added.

Dorothy Shea, the U.S. ambassador to Lebanon, said she witnessed the explosion firsthand. In a tweet, she said, "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."

The blast comes at a time of heightened tension between the Iranian-backed group Hezbollah, which makes up part of the Lebanese government, and neighboring Israel. An Israeli military official told ABC News they had no comment on the blast.

Lebanon is also in a position of severe financial difficulty which has exacerbated sectarian tensions within the country in recent months.

This is a developing story. Please check back for updates.

ABC News' Leena Saidi, Conor Finnegan and Christine Theodorou contributed to this report.