MUMBAI (REUTERS) - Heavy monsoon rains caused the breach of a small dam in western India, washing away dozens of homes and killing at least six people, with 18 missing, a government official said on Wednesday (July 3).

Seasonal rains this week have crippled Mumbai, India's financial centre, disrupting rail and air traffic in the city of 18 million, while wall collapses have killed nearly 30 people.

Tuesday's breach of the Tiware dam in the coastal district of Ratnagiri, nearly 275km south of Mumbai, washed away dozens of homes, an official of the Maharashtra state government said.

"Around 18 people are missing," he added. "Six dead bodies have been recovered."

State officials have asked the National Disaster Response Force to help find the missing.

In every monsoon season, from June to September, India suffers fatal incidents of building and wall collapses, as rainfall weakens the foundations of poorly built structures.