A large blast has hit the Lebanese capital, Beirut, causing widespread damage and injuring many people, officials say.
It is not yet clear what caused the explosion in the port area of the city. Video posted online showed a large mushroom cloud and destroyed buildings.
Hospitals are said to be overwhelmed by casualties.
It comes at a sensitive time with the country's economic collapse reigniting old tensions.
Tensions are also high ahead of the verdict in a trial over the killing of ex-PM Rafik Hariri in 2005. A UN tribunal is due to issue its verdict in the trial of four suspects in the murder by car bomb of Hariri on Friday.
Lebanon's health minister, Hamad Hasan, has spoken of many injuries and extensive damage.
Reuters news agency quotes sources as saying 10 bodies have been pulled from the wreckage.
The cause of the explosion is still not known, but some reports suggest it may have been an accident. Lebanon's National News Agency reported a fire breaking out at what it called an explosives depot at the port.
Local media showed people trapped beneath rubble. A witness described the first explosion as deafening. Video footage showed wrecked cars and blast-damaged buildings.
The latest reports come amid political tension in Lebanon, with street demonstrations against the government's handling the worst economic crisis since the 1975-1990 civil war.
There has also been tension on the border with Israel, which said last week that it had thwarted an attempt by Hezbollah to infiltrate Israeli territory.