Bangkok has been hit by severe flooding after heavy rainfall transformed parts of the Thai capital into stagnant lakes, with about 40 people killed in flood-related incidents, according to the government.

The deaths included people who drowned and several who were accidentally electrocuted, while thousands of residents sought shelter at more than 230 shelters across the city, authorities said, reports The Guardian.

Around 300mm of rain fell in parts of Bangkok over about two days, equivalent to roughly half of London’s average annual rainfall.

Bangkok regularly experiences heavy afternoon downpours during the rainy season, which can briefly flood streets across the city. However, the volume of rainfall this year has left entire neighbourhoods severely inundated.

The flooding has affected areas including central districts with high-rise buildings, where streets can quickly become flooded during heavy rain.

The government has declared a disaster across all 50 districts of Bangkok.

Experts have warned that extreme flooding is likely to worsen across south-east Asia.

Suleemas Kurangkul, a 73-year-old resident of a block of flats whose ground floor stairs are still under water, said last weekend’s rain was not the usual evening storm but was constant, “like all day, all night”.

“The water just kept rising,” said Suleemas, whose flat is above the waterline on the second floor. By the time she and her neighbours received a mobile phone warning, it was too late, and the street-level water was waist-high.

The 1970s Khlong Chan flat compound in north-east Bangkok has been marked by the disaster, with its buildings surrounded by brownish floodwater and only the rooftops of parked cars visible above the surface.

Suleemas said the rain water had receded somewhat. “People are so happy to see the sunshine,” she said. “Yet, the smell is getting stronger. So much debris and rubbish floating all over the place.”

Built on the Chao Phraya River floodplain, Bangkok relies on canals, pumps and dikes to drain water, but concrete construction has destroyed much of the canal network, leaving the city struggling to cope as all 50 districts face a declared flood disaster, with one man arrested for riding a jet ski along a main road.

“It’s a lesson,” said Chaleerat Chamrasporn, 55, a resident. “The kids are into doomsday-themed content, so now they can see what the ‘end of the world’ is actually like, or rather, that this is just the beginning.”

Flooding has disrupted Bangkok’s Suvarnabhumi airport, with about half of Thai Airways’ workforce unable to report for work at one point, causing luggage to pile up and flights to be cancelled, while many schools have closed and severe gridlock has left even residents in less-affected areas stranded at home.

Thailand’s Prime Minister Anutin Charnvirakul told reporters that Bangkok’s metropolitan area was still at risk from flood waters flowing in from ​the north, and said a room had ‌been set up to monitor ‌the situation. Thailand’s weather ⁠agency has forecast more ​heavy rain for next week.

“In central Thailand, I can see from my maps, we have already seen a small but significant trend towards extreme rainfall,” said Nikolaos Skliris, an ocean scientist at the University of Southampton who has studied heavy rain in the region.

“In the long-term, all models show this will be amplified – more rainfall, and more extreme rainfall.”

It is too early for scientists to attribute these particular rains to climate breakdown without doing a study. They were caused by a low-pressure system that moved from an unusually warm South China Sea over Cambodia and Vietnam before getting stuck above Bangkok, which was fairly cool, data from Copernicus Climate Pulse showed.

The picture is complicated by the emergence of an abnormally strong El Niño, a cyclical weather pattern that brings record heat and more violent extremes around the world. Its presence typically leads to drier summer conditions in south-east Asia but recent research suggests it still exacerbates days with extreme rainfall, as reported by The Guardian.

Naim Laeni, a consultant and part-time university lecturer who co-authored a study on Bangkok’s flood resilience, said authorities had underestimated the intensity and duration of the rainfall.

Bangkok’s drainage canals can handle about 60mm of rain an hour, rising to 80mm in upgraded sections, but localised rainfall exceeded those limits.

“The government did not communicate the seriousness,” Laeni said. “Usually in Bangkok we receive heavy rain for a few hours, not for days.”

The same weather system has caused flash floods and landslides in neighbouring Myanmar, where rescue efforts have been complicated by blocked roads and the ongoing civil war. A landslide in the southern village of Ka Det Nge Htein killed nine people, while eight others remain missing under mud in another village, according to local officials.

In Bangkok, pumping stations are operating at full capacity, but authorities said it could take days for the floodwaters to fully drain.