At least 19 people were killed on Friday after a minibus they were travelling in plunged into a river in southern Tanzania, police said. The accident occurred on a highway in Mbeya, a town in the south of the country, Mbeya regional police chief Ahmed Msangi said in a statement. Of those killed, 18 died on the spot and one died in hospital. Three more were injured.Traffic accidents are common in the east African country, where buses are the main form of public transport and are often crowded and travel on poor roads.Critics say the authorities fail to enforce basic traffic rules. Police say accidents are often caused by speeding.Police officials said more than 100 people have been killed in road accidents in the past month, mostly involving buses.