Rescuers and onlookers stand at the spot of a wall collapse in Mumbai, India, on Tuesday.

Monsoon rains caused wall collapses that killed 27 people in India on Tuesday, as a second day of bad weather disrupted rail and air traffic in the financial capital Mumbai, prompting officials to shut schools and offices, though markets were open.

During every monsoon season, which runs from June to September, India experiences fatal incidents of building and wall collapses as rainfall weakens the foundations of poorly-built structures.

Heavy rain brought a wall crashing down on shanties built on a hill slope in Malad, a western suburb of Mumbai, a fire brigade official said, killing 18 people.

"Rescue work is still going on," the official added. "So far we have rescued more than two dozen people."

Onlookers stand behind a portion of the broken wall that collapsed in Mumbai. Punit Paranjpe/AFP

Three people died when a school wall collapsed in the city of Kalyan, 42 km (26 miles) north of Mumbai.

In the nearby western city of Pune, six people were killed in a wall collapse on Tuesday, a fire brigade official said, after a similar incident on Saturday killed 15.

Mumbai is looking to turn itself into a global financial hub but large parts of the city struggle to cope with annual monsoon rains, as widespread construction and garbage-clogged drains and waterways make it increasingly vulnerable to chaos.

More than 300 mm (11.8 inches) of rain fell over 24 hours in some areas of Mumbai, flooding streets and railway tracks, forcing the suspension of some suburban train services, which millions of commuters ride to work each day.

Commuters walk on waterlogged railway tracks after getting off a stalled train in Mumbai. Francis Mascarenhas/Reuters

About 1,000 people stranded in low-lying areas of the city were rescued after a swollen river began to overflow, municipal authorities said.

As weather officials forecast intermittent heavy showers and isolated extremely heavy rainfall, authorities called a holiday for government offices and educational institutions.

"Rain is expected to remain intense even today," city authorities said on Twitter. "We request you to stay indoors unless there's an emergency."

Financial markets were open on Tuesday, though trading volumes were expected to be lower than normal. Many firms asked employees to work from home.

The main runway at Mumbai airport, India's second biggest, was closed from midnight after a SpiceJet flight overshot the runway while landing, an airport spokeswoman said.

The secondary runway is operational, but 55 flights were diverted and another 52 were cancelled due to bad weather, she said.

In 2005, floods killed more than 500 people in Mumbai, the majority in shantytown slums home to more than half the city's population.

Reuters