Due to dry westerly winds blowing across from Pakistan to northwest India at lower levels of the atmosphere, a heat wave is expected to sweep through Delhi, Punjab, Haryana, Chandigarh, north Rajasthan, Uttar Pradesh and north West Madhya Pradesh during the next two days, the India Meteorological Department said on Thursday.

For the plains, a "heat wave" is declared when the maximum temperature is more than 40 degrees Celsius, and at least 4.5 degrees above normal.

A "severe" heat wave is declared if departure from normal temperature is more than 6.5 degrees Celsius, according to the India Meteorological Department (IMD).

"Usually, the capital witnesses heat waves till June 20. The increase in the maximum temperature this time can be attributed to the delay in the arrival of the monsoon," said Kuldeep Srivastava, the head of the IMD's regional forecasting centre.

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On Tuesday, Delhi witnessed the first severe heat wave of the year with the maximum temperature at Safdarjung Observatory, which is the official benchmark for the national capital, rising to 43 degrees Celsius, the highest so far this year.

The monsoon usually reaches Delhi by June 27, but has been delayed. The southwest monsoon had hit Kerala on June 3 after a delay of two days.

Meanwhile, an unprecedented heat wave has also hit North America with dozens of people dying in Canada. The US states of Washington and Oregon have also been affected.