The temperature rose to a seven year high of 42.1 degrees C in the metropolis on Saturday, making it the hottest day this summer, even as the Met office extended the heat wave warning by another 24 hours.
"We have renewed the heat wave warning for Kolkata, its neighbourhood and for entire south Bengal for another 24 hours with this condition likely to continue for at least a day," Centre Director G C Debnath told PTI.
The city had recorded 43 degrees C in 2002. "The city had the highest-ever record of 43.7 degrees C in 1958," Centre sources said.
The humidity was at a high 87 per cent.
In Bankura and West Midnapore districts, the mercury climbed to 45 degrees C and 44 degrees C respectively, the sources said.
The upper circulation of moist air had gone and there was incursion of hot and dry winds from Chhattisgarh and Jharkhand, leading to the heat wave conditions, Met officials said.
Meanwhile, 25 persons, affected by the heat, were admitted to hospital with diarrhoea and vomiting symptoms at Anachuri village in Bankura district, a report said.