The A14 at Beyton is partially blocked eastbound around Thurston because of a crash.
A spokesman for Suffolk police said a Land Rover-style vehicle had been towing a trailer with another similar vehicle on it.
Just before 5pm the vehicle on the trailer has fallen off and landed on its roof.
The inside lane of the eastbound carriageway has been closed while recovery takes place.
The spokesman said the closure would likely be in place for some time as work will need to be done to the vehicle before it can be righted onto its wheels.
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