Voting in India’s general election, a six-week-long referendum on Prime Minister Narendra Modi’s decade in power, came to a close on Saturday as much of the country’s populous north was gripped by a deadly heat wave.

Results will be tallied and announced on Tuesday.

Mr. Modi, his power deeply entrenched, is seen as likely to win a third consecutive term as prime minister, which would make him only the second leader in India’s nearly 75 years as a republic to achieve that feat. Exit polls released after the last round of voting suggested a comfortable return for his Hindu-nationalist Bharatiya Janata Party, or B.J.P.

A newly united opposition has put up a fight, rallying against Mr. Modi’s divisive politics and management of India’s deeply unequal economic growth. But the exit polls indicated it was struggling to significantly cut into the sizable majority in the 543-seat Parliament held by Mr. Modi’s party.

In a message of thanks after the voting closed, Mr. Modi expressed confidence that “the people of India have voted in record numbers to re-elect” his government. But Mallikarjun Kharge, the president of the largest opposition party, the Indian National Congress, played down the exit polls as “government surveys” and said the official results will show that his alliance was ahead.

The election, held in phases over a month and a half, is the largest democratic exercise in the world, with more than 950 million eligible voters. The last stretch of the campaigning drew large rallies even as northern India baked under an intense heat wave, with temperatures frequently exceeding 110 degrees Fahrenheit, or more than 43 degrees Celsius.

At least 19 poll workers have died from heat strokes or other health complications resulting from the heat in recent days.