Swathes of north India are sweltering under the longest heatwave on record, triggering widespread breakdowns in the supply of electricity and increasingly angry protests over the government's failure to provide people with basic services.

The power crisis and heatwave, which some activists say has caused dozens of deaths, is one of the first major challenges for Prime Minister Narendra Modi, who was elected three weeks ago partly on promises to provide reliable electricity supplies.

Hot June in India. Credit:AFP

In Delhi, where temperatures have hit 45 Celsius for six days straight, residents marched through the streets in protests organised by opposition parties on Thursday. In the north of the city, people enraged by night-long outages clashed with police and torched a bus, media reported.

Delhi is suffering staggered cuts as power companies ration spikes in demand as people crank up air coolers to fight the heat. Modi has inherited the shortages from his predecessors, and power distribution is partially the responsibility of state governments.