UPDATE 1-Riyadh industrial building hit by explosion

(Adds report saying explosion at petrol station)

RIYADH, Nov 1 (Reuters) - An industrial building in eastern Riyadh was almost entirely destroyed by a large explosion on Thursday, a Reuters witness said.

The building was almost levelled by the blast, with one corner left standing, the witness said. Nearby vehicles were on fire and at least five fire engines were arriving at the scene.

The reason for the explosion was not immediately clear.

Al Arabiya television reported that the blast was caused by a fuel truck exploding at a petrol station, and that there had so far been no news of casualties. The report could not immediately be confirmed.

(Reporting by Angus McDowall; Editing by Andrew Torchia)