At least nine people were killed when a tractor-trolley fell into a canal in Polonnaruwa in the central province of Sri Lanka Friday, police said.Police said the tractor, usually used for farming, was transporting on a trolley a group of people when the driver lost control over the vehicle and it fell into the canal, Xinhua reported.Police spokesman Ajith Roahan said that eight other people were injured in the accident and were admitted to hospital.It was not clear if the canal was dry.Those killed were four women, two men, two children and a baby, the police spokesman added.Tractor-trolleys are a common mode of transport in rural areas in Sri Lanka where passenger buses and trains do not operate.