A large blast has hit the Lebanese capital, Beirut, ahead of the verdict in a trial over the killing of ex-PM Rafik Hariri in 2005.
Reports say the explosion was in the port area of the city, with unconfirmed reports of a second blast. The authorities fear many casualties.
Video posted online showed a large mushroom cloud and extensive damage.
A UN tribunal is due to issue its verdict in the trial of four suspects in the murder by car bomb of Hariri.
All four are members of the Iranian-backed Hezbollah group, which has consistently denied any role in Hariri's death. The verdict is due on Friday.
The possible second explosion was reported to be at the Hariri residence in the city.
Lebanon's health minister has spoken of many injuries and extensive damage.
Local media showed people trapped beneath rubble. A witness described the first explosion as deafening.
The cause of the blast is not yet clear.
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.