Beirut's downtown streets were littered with debris and damaged vehicles after a massive explosion rocked the Lebanese capital Tuesday, August 4, killing more than 100 people dead and at least 4,000 injured.

Officials said they expected the number of victims to rise as crews worked their way through rubble of damaged buildings and people searched for missing family and friends.

The exact cause of Tuesday’s blast was not clear, but Lebanese officials put the focus on what they said was tons of ammonium nitrate that had been stored at port warehouses for the past six years.

The explosion took place in the evening, sending a huge mushroom cloud into the sky and shockwaves that blew out doors and windows far from the port, overturned cars and damaged numerous buildings.

In the aftermath, hospitals were overrun with people seeking care.

The international community has responded with both condolences for the dead and offers to help the people of Beirut with recovery efforts.

Prime Minister Hassan Diab declared Wednesday a day of mourning in Lebanon.