The incident happened on the overpass above the Jedi Hak intersection on southbound Phetchakasem Rd, said Pol Capt Nareerat Harnnarong, a duty-officer at Muang police station.
Police and rescue workers rushing to the scene found 21 cars, pickup trucks and trucks involved in the crashes, which led to heavy traffic backups in the area.
Fourteen people were injured, 10 slightly. The wounded, mainly by broken glass, were sent to Ratchaburi Hospital.
Phalathorn Thapthimsuk, 23, driver of a pickup truck loaded with chicken fat in plastic bags, said he was travelling from Kanchanaburi to Phetchaburi at the time. While he was driving down the overpass, a tarpaulin covering the back of his truck suddenly blew away, causing many bags of fat to fall onto the road.
The bags broke and the chicken fat spilled onto the traffic lanes. Many motorists applied their brakes, causing them to lose control on the slippery road and crash into other vehicles.
Rescue workers later cleared up the scene.
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