An Iranian passenger plane carrying 168 people has nose-dived into a field shortly after take-off. The crash shredded the aircraft and killed everyone aboard in Iran's worst air disaster in six years.

Iranian soldiers gather at the crash site of the Caspian Airlines plane, which fell into farmland near the city of Qazvin, northwest of Tehran on July 15, 2009. [Liang Youchang/Xinhua]

The impact of the Caspian Airlines jet ploughed a deep, long trench into agricultural fields outside the village of Jannat Abad.

Witnesses say the plane's tail was on fire before it went down.

Local resident, said, "I got out of my car to pour water in it when I heard a roaring sound from the sky. I thought it was not cloudy enough to hear thunder. As I looked above I saw the rear section of the airplane had caught fire and then it crashed."

Smoke smoldered from the pit for hours as emergency workers searched for data recorders and other clues to the cause of the crash.