Mumbai's city council ordered schools and colleges shut Monday as a precautionary measure, reporting that the India Meteorological Department (IMD) had warned of "heavy to very heavy rainfall".
Many streets were under water in the coastal city after hours of heavy rain, with several bus and train services suspended.
In Bihar, 10 people were killed in separate lightning strikes on Sunday, state Chief Minister Nitish Kumar said in a statement, asking people to "stay indoors during bad weather".
Monsoon rains across South Asia from June to September offer respite from the summer heat and are crucial to replenishing water supplies, but also bring widespread death and destruction.
The number of fatal floods and landslides has increased in recent years, however, and experts say climate change is exacerbating the problem.
Floods have also swamped the northeastern state of Assam, with eight people killed in the last 24 hours, Assam's Disaster Management Authority said Sunday.
That takes the death toll from the downpours since mid-May to 66.
In the northern state of Uttarakhand, authorities issued warnings of heavy rain.
The ferocious storms also bring frequent lightning strikes.
In 2022, nearly 3,000 people died from lightning strikes across India, according to the national crime records bureau.
