Mumbai was hit by heavy rain this morning as monsoon arrived, inundating low lying areas and disrupting local trains and flights. At least 20 domestic flights have been delayed and one cancelled; 12 international flights are also late, while two stand cancelled. Local trains are running 15-20 minutes late, officials said. "Parts of a wall fell on the tracks this morning. It was removed immediately and for some time, trains on the down slow line were diverted to the fast line," Central Railways spokesperson Sunil Udasi said. Heavy rain has been forecast in Mumbai till tomorrow.