NEW DELHI, June 11 (Reuters) - Hot and dusty desert winds have caused a heatwave across the plains of northern India, killing 74 people over the last week, officials and local media reports said on Monday.

Most of the dead were beggars, homeless and people working in the open hit by sunstrokes and dehydration.

The Press Trust of India put the toll at 74, including 15 in the western desert state of Rajasthan and nine in the northern state of Uttar Pradesh during the weekend.

Temperatures peaked on Saturday, reaching 48.9 degrees Celsius (120 Fahrenheit) in Ganganagar in the desert state of Rajasthan, said S.C. Bhan, director at the Regional Meteorological Centre in New Delhi.

"It is a heatwave. After the next two days it will be over," Bhan said, adding that it was caused by winds from the Thar desert, which spreads from Rajasthan into neighbouring Pakistan.

In New Delhi, the mercury touched a season high of 44.9 degrees Celsius (113 Fahrenheit) on Saturday, Bhan said.

People dozed the afternoon away under trees and on shady pavements while those at home stayed close to their air-conditioners when there were no power cuts -- a frequent occurence over the weekend.

"It's unbearable from the moment I set up shop," complained Som Dutt, a streetside barber in Delhi, who said business was slow because no one wanted to sit in his unshaded chair.

Delhi's markets were nearly deserted with people seeking refuge in one of the city's air-conditioned shopping malls. Newspaper reports said two flights out of Delhi were delayed as aircraft developed technical problems due to the heat.

Watermelon sellers in Rajasthan reported brisk business.

"I used to sell 50 to 70 watermelons in a day, but now I am selling over 100," said Ram Singh in Jaipur, the state capital. (Additional reporting by Geetinder Garewal in Chandigarh and a Reuters reporter in Jaipur)

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