"Southwest monsoon was vigorous over interior Karnataka and active over coastal Karnataka on Monday," the Bengaluru centre of India Meteorological Department (IMD) said on its website.
Heavy rainfall was observed in the state's coastal districts of Udupi, Uttara Kannada and Dakshina Kannada, and interior districts of Kodagu, Hassan, Chikkamagaluru.
The heavy monsoon inundated low-lying areas, uprooted several trees and damaged roads in the coastal and south districts of the state.
Parts of Udupi, Uttara Kannada, Hassan and Chikkamagaluru received very heavy rainfall measuring over 13 cm on Monday, according to the data from IMD.
Heavy rains also caused landslides near the hilly town of Yedakumeri in the midst of Western Ghats in Hassan district, about 180km west of Bengaluru, leading to two trains being diverted.
All the passengers of the express train en route Karwar in Uttara Kannada district, about 520km northwest of Bengaluru, were stranded at Hassan and later reached their destined towns and cities in state-run buses.
Another train Karwar-Yesvantpur Express which runs between the port city of Karwar and Bengaluru, was re-routed due to the landslide.
The weather office predicts heavy rain to continue through the week in coastal and south interior districts.