A massive explosion at a port in the Lebanese capital Beirut killed at least 100 people and injured more than 4,000 others on Tuesday, according to the Lebanese Red Cross. 

Prime Minister Hassan Diab said that a large stockpile of 2,750 metric tons of ammonium nitrate in a warehouse at the port had caused the second, larger explosion.

Witnesses also reported seeing an orange cloud like that which appears when toxic nitrogen dioxide gas is released after an explosion involving nitrates.

Meanwhile, the Red Cross said that the death toll could still rise as crews search for people buried under the rubble. 

Smoke was still rising from the port on Wednesday morning. 

"It is unacceptable that a shipment of 2,750 tons of ammonium nitrate has been present for six years in a warehouse, without taking preventive measures," Diab said at a defense council meeting, according to his spokesman later briefing reporters.

"We cannot remain silent on this issue...I will not rest until I know who was responsible for what happened and give them harshest punishment," Diab said. 

Ammonium nitrate, a chemical compound, has many uses, from agricultural fertilizer to mining charges or indeed bomb-making. Lebanese officials were saying in this case that it was a large contingent of agricultural fertilizer that had been stored in the warehouse ever since it was seized from a cargo ship in 2014, awaiting either auction or proper disposal.

"Facts about this dangerous warehouse that has been there since 2014, i.e. for 6 years now, will be announced," Diab said, adding that he would not pre-empt investigations into the blasts.

"At the moment, we are focusing on handling the disaster, pulling the martyrs out, and treating the wounded."

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'Hospitals are overloaded'

The Lebanese Red Cross said over 30 teams were responding to the incident.

 The blast damaged buildings across the capital, leaving bodies buried in the rubble, officials said. Smoke was seen billowing across the city. 

Residents in Cyprus, some 110 miles (180 km) across the sea from Beirut, reported hearing the blast.

President Michel Aoun scheduled an emergency Cabinet meeting for Wednesday and said a two-week state of emergency should be declared.

For hours after the explosion, ambulances carried away the wounded and hospitals quickly filled beyond capacity, appealing for blood donations. One hospital reported over 500 patients had arrived.

DW's Bassel Aridi visited a hospital. "What I saw in the hospital was so dramatic. All the hospitals have announced that they are totally overloaded."

"People are asking for their loved ones on social media," he added. "The destruction and ruins are huge." 

The German Foreign Ministry said that German citizens were among those injured.

"We are shocked by the pictures from Beirut," they wrote on Twitter. "Workers from our embassy are among those who are injured. Our thoughts are with the relatives of the victims. Germany is standing by Lebanon in this difficult time. We are looking at what help we can offer."

Israel and Hezbollah both say not a rocket attack

Israel said it had nothing to do with the explosion, urging "caution around speculation." Hezbollah also said it had no indication of Israeli involvement.

Tensions have been high between the two neighboring countries; Israel said late in July that it had thwarted an infiltration attempt by Hezbollah gunmen. The most recent war between Lebanon and/or Hezbollah and Israel took place in 2006.

Lebanon is also currently in the grip of severe economic turbulence, with many people taking to the streets in recent months to protest the financial situation.

Diab declared that Wednesday would be a national day of mourning for the victims of the explosion.

International condolences poured in following the explosion. The European Union, the US, Saudi Arabia and Iran announced they would help Lebanon in any way necessary. 

mvb, ed/msh (AFP, AP, dpa, Reuters)

This story is subject to frequent updates and alterations as the situation develops.