MUMBAI (Reuters) - A rush hour stampede killed at least 22 people and wounded 36 on Friday during a sudden monsoon downpour at a busy railway station in India’s commercial hub of Mumbai, government and emergency officials said.

India has the world’s fourth biggest rail network, but it is grappling with underinvestment and overcrowding, especially in the city of 20 million where rail accidents have killed more than 3,000 people in each of the last three years.

The cause of the stampede on a tiny bridge at the central Elphinstone Road station was being investigated, a police official at the accident site said.

“Some of the injured are in serious condition,” Deepak Sawant, the health minister of the western state of Maharashtra of which Mumbai is the capital, said at a hospital where the injured were taken.

The stampede, at a station recently renamed Prabhadevi, took place after the cloudburst caught commuters off guard, sending scores scurrying for cover under a pedestrian overbridge, said Akash Koteja, one of those injured.

“Trains were rolling in and some people wanted to get out of the station, but others were not making way. When a few tried, it led to a stampede,” Koteja added.

The bridge is usually crowded at that time of day, as it also provides an exit route for passengers disembarking at an adjoining railway station, he added.

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Manish Mishra, a witness who helped some of the injured, said the situation was worsened as officials did not respond immediately, or take steps to control the crowd.

Emergency officials responded rapidly, state officials said, however.

“Immediately after the incident, rail, police and hospital authorities rushed to provide treatment to those injured,” state minister Vinod Tawde told reporters.

Railways Minister Piyush Goyal, who was on a visit to Mumbai, has ordered an enquiry into the incident led by a top railway safety official, he said on social network Twitter.

Over the last two months, Mumbai has reeled from devastation caused by heavy seasonal monsoon rains.

Last month a deluge killed 14 people, wrecked homes and caused chaos. Torrential rain was also blamed for the collapse of a 117-year-old building that killed 34 people, and water-logging last week that disrupted flights after a passenger jet overshot a runway.

Prime Minister Narendra Modi and Finance Minister Arun Jaitley sent Twitter condolence messages to stampede victims’ families.

Hundreds of social media users angered by the event questioned the government’s priorities, targeting Modi’s ambitious $17-billion plan for a bullet train to link Mumbai with Ahmedabad in neighboring Gujarat state.

Many tweets urged the government to fund basic rail upgrades instead.