Scientists say this is part of climate that's becoming a worldwide phenomenon.

The country is witnessing its worst-ever heat wave, with four cities in north India on a record high. Starting with national capital Delhi, Churu in Rajasthan and Banda and Allahabad in Uttar Pradesh have witnessed temperatures of 48 degrees Celsius and above.

Churu has crossed 50 degrees twice in the last week -- a whopping 8 degrees above its normal temperature at this time of the year.

Banda is close behind at 49.2 degrees, Allahabad at 48.9. Delhi touched 48 degrees -- a record high for June -- on Monday.

Heat wave is declared when temperature remains at 45 degrees Celsius and above for two days running. It gets a "severe" tag when mercury touches 47 degrees.

Heat waves have been becoming increasingly frequent over the last years.

Since 2004, the country has experienced 11 of the 15 warmest years. Last year was the sixth-warmest since 1901, when preserving weather records started in the country.

Last week, 11 of the 15 hottest places in the world were located in India, the rest were in neighbouring Pakistan, weather monitoring website El Dorado reported.

Scientists say this is part of climate change that's becoming a worldwide phenomenon and is likely to become more frequent. Environmental activists have suggested that India put in place a plan to tackle heat waves that are costing hundreds of lives every year.

Since 2010, more than 6000 people have died in heat waves in the country, the Lok Sabha was told last year by health minister Harsh Vardhan.

On Tuesday, four people died on board a train, the Kerala Express, while it was passing through Jhansi. A railways spokesman said they suspected the heat to be a factor.