At least 54 people died in a district in the northern Indian state of Uttar Pradesh over the last few days, the Times of India newspaper reported on Monday, as authorities probed if the loss of lives was due to the heat wave in the region.
Another 45 people died in neighbouring Bihar state, local newspapers reported.
The Indian Meteorological Department (IMD) issued a red alert warning last week for extreme heat in some regions of the country, including Uttar Pradesh and Bihar.
The government said it was investigating the cause of the deaths that occurred over three days last week in Uttar Pradesh's Ballia district, about 970 km southeast of New Delhi.
"Deaths have occurred in the district but it is very difficult to say if that happened due to the heat wave," said Ravindra Kumar, the top administrative official of the district, told Reuters, without confirming the number of deaths.
"A few of the deaths are related to old age, while some have different reasons. There is no concrete evidence of heat wave behind these deaths."
The government fired Diwakar Singh, the chief medical official at the main state hospital in Ballia, for saying that the deaths were due to heat.
The state's deputy chief minister, Brajesh Pathak, said on social media that Singh had been removed from his position for making an "irresponsible statement".
Temperatures have soared close to 45 degrees Celsius in recent days in Ballia with a severe power crisis compounding the situation.
In Bihar, 45 people lost their lives due to heat-related illnesses, the Hindustan Times newspaper reported. Officials in Patna, the capital of Bihar, did not answer phone calls.
While the heat wave was expected to continue in some regions on Monday, parts of India's northeastern Assam state reeled under floods triggered by heavy rains.