In a statement after the election, Hasanli condemned what he called "total falsification and rude trampling on the people's rights."
"Already now the legitimacy of the election can be called into question," he said.
Earlier in the day, Hasanli said that his supporters registered cases of ballot stuffing at a number of polling stations. "Regrettably, many government officials are involved in falsification, becoming accomplices of a grave crime," he said.
The Central Election Commission chief insisted that the vote was clean. International election monitors are to issue their report Thursday.
International rights groups have accused Aliyev of pressuring and harassing government critics, leaving them little chance to campaign. The government, however, loosened restrictions ahead of the ballot, withdrawing its longtime ban on rallies in the center of the capital.
Aliyev has ruled the ex-Soviet nation of 9 million since 2003, succeeding his father, Geidar Aliyev, who had been at the helm for most of the previous three decades, first as Azerbaijan's Communist Party boss during the Soviet times, then as its president.
The younger Aliyev has presented himself as a guarantor of stability, an image with broad appeal in a nation where painful memories are still fresh of the years of turmoil that accompanied the 1991 breakup of the Soviet Union.
A six-year war with neighboring Armenia over the disputed territory of Nagorno-Karabakh left ethnic Armenian forces in control of Nagorno-Karabakh and neighboring areas in Azerbaijan and turned 1 million Azerbaijanis into refugees.
The Azerbaijani leader has shown little tolerance for dissent and extended his rule through elections criticized by Western observers. At the same time, he has firmly allied the Shiite Muslim nation with the West, helping to secure its energy and security interests and to offset Russia's influence in the strategic Caspian region.
Under Aliyev, Azerbaijan has basked in oil riches that have more than tripled its GDP and helped bolster his popularity. The State Oil Fund that accumulates oil revenues held $34 billion at the start of the year.
After hearing the exit poll data, hundreds of Aliyev's supporters carrying national flags and pictures of the president took to the streets, some dancing to popular music. Motorists and bikers drove around the city, waving Azerbaijani flags and honking horns.
"We all are very happy and think that Azerbaijan in the coming five years will continue to prosper and will become the best country in the world," Baku resident Samira Kulieva said.
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Sophiko Megrelidze contributed to this report.
