Heavy rainfall in India's financial capital, Mumbai, has disrupted the lives of millions of people, submerging roads and leading to flight and train cancellations.

Many parts of the city remain inundated in waist-deep water, with videos showing residents swimming through waterlogged roads as garbage gushed out from clogged sewers.

Authorities on Tuesday rescued 600 people who got stuck on an overcrowded monorail system that stopped mid-journey. At least 23 had to be treated for suffocation, officials have said.

Monsoon rains are common in Maharashtra state, where Mumbai is located, around this time of the year.

But the region is experiencing particularly heavy rainfall this time. At least 21 people have died in rain-related accidents across the state this week.

In just four days, Mumbai has seen 800mm of rainfall, according to the India Meteorological Department, which is well above the average rain recorded in August.

India's weather department has issued a red alert for the city and its neighbouring districts, predicting very heavy rains to continue on Wednesday, but has said the situation would improve later in the week.

Most schools and colleges are shut and some 350 people have been shifted from the city's low-lying areas to temporary shelters.

Mumbai's local trains - a lifeline for millions of commuters - have seen heavy disruptions with thousands of people waiting on platforms on Tuesday as services were delayed for hours.

"Trains scheduled for last night have left this morning, and those supposed to leave this morning have been delayed to later," a passenger told news agency ANI.

Flight operations to and from the city's international airport have also taken a hit, with 50 flights reportedly cancelled over the past few days.

"While we want your journey to be as hassle-free as possible, Mother Nature has her own plans. With heavy rains expected again in Mumbai, there's a chance this could lead to air traffic congestion and impact flight operations," budget carrier IndiGo said on X.

Meanwhile, chaos erupted on Tuesday after a monorail system, which was reportedly full far beyond its capacity, halted mid-track.

A passenger who was on the train told BBC Marathi that with the air-conditioning switched off, passengers tried to open the doors to call for help.

Fire department and police teams had to use cranes to bring stranded passengers down from the elevated tracks.

A preliminary investigation suggested the incident took place due to "overcrowding in the train", according to reports.

Opposition lawmakers have blamed the government for being ill-prepared to handle the situation.

Aaditya Thackeray of the opposition Shiv Sena (UBT) party said several areas, including Mumbai, were witnessing an "absolute collapse of governance".

He alleged that the government had done "zero planning" despite red alerts being issued, pointing out that the city's airport was flooded on Tuesday and new water-logging spots had emerged - particularly around recently built infrastructure.

Several citizens also took to social media, criticising the city's collapsing infrastructure and poor planning.

Mumbai is one of India's richest cities, significantly contributing to the country's GDP, industrial output and trade.

Home to more than 12 million people, it has long attracted migrants from across the country who come in search of better opportunities.

While the city has seen a bevy of infrastructure upgrades in recent years - including coastal roads, sea bridges and a new metro system - experts say investments to improve ageing drainage systems and climate-resilient infrastructure have not kept pace with the growing population.