The northern section of the grain silos damaged two years ago by a blast at the Beirut port collapsed early on Tuesday after warnings the structure was leaning too far to stay up.
The crash sent a cloud of brown-grey dust billowing over the waterfront, the LBCI television station reported. There were no immediate reports of injuries.
The huge explosion at the port on August 4, 2020, killed more than 220 people and gutted the northern section of the grain silos, leaving wheat and corn spilling out in the sun.
Recently, a fire had been smouldering in the silos for weeks, which officials said was the result of summer heat igniting fermenting grain left rotting.
Part of the structure collapsed on July 31 and another section fell on August 4, the second anniversary of the blast.
On Sunday, the health ministry said dust samples from around the port showed that the air contained high amounts of common mould, which would not be dangerous unless inhaled in large quantities over a long period of time.
Hurricane Melissa slammed into Cuba early on Wednesday, hours after causing devastation in neighbouring Jamaica as the strongest-ever storm on record to hit that Caribbean island nation.
US President Donald Trump said on Wednesday that a US-backed ceasefire in Gaza was not at risk after Israel launched airstrikes in the enclave, which killed 26 people in response to the killing of an Israeli soldier.
South Korea welcomed US President Donald Trump on Wednesday with a replica gold crown and awarded him with the "Grand Order of Mugunghwa", the country's highest decoration, the presidential office said.
Rodrigo Duterte, the former president of the Philippines, has appealed last week's decision by the International Criminal Court to continue its case against him and is seeking his release, court documents showed on Wednesday.
One person was killed on India's eastern coast after Cyclone Montha made landfall around midnight, with heavy rain and gusty winds also damaging crops and utility poles, officials said on Wednesday.