People living in Kalutara,Madurawala,Dodangoda, Horana, Palindanuwara, Bulathsinhala, Ingiriya, Millaniya, Kirialla, Kuruvita,Alapatha and Ratnapura DS Divisions have been asked to evacuate with immediate effect.
The Disaster management Centre said the announcement was made due to overflowing of the Kalu River.
People have been asked to remain in safe locations until water levels recede to safe levels.
It also added that inclement weather conditions would continue for a few more days.