Dozens of people have died in Pakistan, where a severe heatwave has coincided with the start of Ramadan.

The southern city of Karachi, with a population of 15 million, is sweltering in temperatures hitting 44 degrees Celsius.

Local media reports say that up to 100 people have died of heatstroke since the weekend.

Heatstroke occurs when the body overheats in prolonged exposure to high temperatures. The condition leads to organ and muscle failure and is exacerbated by dehydration.

The soaring temperatures in Karachi have come at the start of the holy month of Ramadan, which sees many Muslims abstain from all food and water during daylight hours.

According to tradition, people who are elderly or have a medical condition are exempt from the expectation to fast.

On social media, young Karachi residents have suggested banding together to deliver water to labourers during the heatwave.

There has also been debate online about the need to plant more trees in Karachi, which suffers from a lack of green spaces.

In 2015, a catastrophic heatwave across Pakistan killed more than 1,000 people, many of them homeless.

In a 2017 report, the Asian Development Bank named Pakistan as one of the world's most vulnerable countries in light of climate change.

It reported that the duration of heatwaves in the country had increased fivefold in the previous 30 years.

The mountainous north of the country is vulnerable to glacial melt, while rising sea levels, drought and temperature increases are expected to affect the coastal south.