At least 19 people died in a flash flood along a river in southern Thailand, while 20 others were reported missing, police said Saturday. The flood caused by unseasonably heavy rains in Trang province, 670 kilometres south of Bangkok, caught dozens of people by surprise at a popular waterfall for picnicking and swimming, dpa quoted police spokesman Anek Phangleesin as saying. The rainy season had not been expected for another two months and the revellers at the popular waterfall did therefore not expect the river to swell so fast, Anek said. The flash flood came during Thailand's traditional New Year celebration, a long weekend holiday when most people return home to be with family.