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.
An Israeli air strike has killed at least three people in the Gaza Strip on Monday, local health officials said, in the latest round of violence since a US-brokered ceasefire took effect more than five months ago.
Spain has closed its airspace to US planes involved in attacks on Iran, a step beyond its previous denial of use of jointly-operated military bases, Spanish newspaper El Pais reported on Monday, citing military sources.
A United Nations peacekeeper has been killed in southern Lebanon overnight, prompting condemnations on Monday after a weekend in which Lebanese journalists and medics were killed in Israeli strikes.
Kuwait's Ministry of Electricity, Water, and Renewable Energy has announced on Sunday that an Iranian attack has killed one worker and damaged a service building at one of its power and water distillation plants.
Iran said it was ready to respond to a US ground attack, accusing Washington on Sunday of preparing a land assault even as the Trump administration sought talks and as regional powers met in Pakistan to try to end the conflict.