As a precautionary measure, the state government declared a public holiday for Mumbai.
According to officials, the compound wall of a school in Pimpripada in Malad suburb collapsed on some adjoining hutments around 1 a.m. in which the toll went up to 19 from the previous 13.
National Disaster Response Force (NDRF), Mumbai Fire Brigade and other agencies were engaged in massive rescue operations to rescue those trapped in the rubble.
Chief Minister Devendra Fadnavis told the state assembly that at least 75 people were injured in the incident as Mumbai received the highest 24-hour rainfall in July since 1974.
Earlier on Tuesday, the compound wall of the Sinhagad College in Pune crashed on some hutments beside, killing at least seven persons, and NDRF teams were at the site to retrieve those still feared trapped in the debris.
Two persons who were trapped inside a SUV in the flooded Malad subway since last night were found dead on Tuesday.
In the adjoining Thane district, three persons were killed when the boundary wall of National Urdu School crashed in Kalyan town and several more were injured. Besides, two persons were washed away in flood waters in an overflowing river in Jawahar.
The Indian Navy's team of divers from INS Tanaji deployed rubber boats, life-jackets, lifebouys and rescued over 1,000 people stranded in Krantinagar slums in Kurla, north-east Mumbai.
Many parts of Mumbai and suburbs, as well as towns in Raigad, Thane and Palghar districts saw people struggling to safety in waist-deep waters, vehicles submerged, several tempos, trucks and heavy stranded on roads adding to traffic snarls.
At least 150 BEST buses in Mumbai were also submerged and stranded at various locations in the city since Tuesday morning.
The IMD has predicted extremely heavy to very heavy rains in parts of coastal Konkan. The Maharashtra government declared a public holiday for Mumbai city and BrihanMumbai Municipal Corporation (BMC) Commissioner Pravin Pardeshi ordered all schools and colleges shut for the day.
When parts of Mumbai experienced a lull in rains since noon, thousands of harried people rushed out of their homes to buy stocks of vegetables, fruits, groceries, milk in markets which were charging higher rates.
( With inputs from IANS )