Announcing Mr Reddy's death, India's home minister P Chidambaram said: "It is not possible to say why the helicopter crashed."
He said preliminary investigations showed that the helicopter, which was heading south, had changed direction and hit a small hill, east of Kurnool.
Mr Chidambaram said the "charred" bodies of the chief minister, his personal assistant, security officer and two pilots were being retrieved from the crash site.
"We are in deep mourning. There is a deep sense of shock and loss," Mr Chidambaram said.
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'Deep regret' at India politician's death
Congress party spokesperson Jayanthi Natarajan told a local television channel that Mr Reddy was a "dynamic leader" and his death was "tragic".
Television footage showed Mr Reddy's family and supporters crying after news emerged that there had been no survivors in the crash.
Thursday's discovery of the helicopter on a hill some 70km (43 miles) east of Kurnool follows a massive search and rescue operation launched by the state government.
Remote forest
Rain reduced many areas to mud, making the search difficult.
The Bell helicopter carrying Mr Reddy was on what should have been a two-hour flight from Hyderabad's Begumpet airport.
It took off at 0845 IST (0315 GMT) on Wednesday bound for the village of Anupally in Chittoor district.
The aircraft went missing over Kurnool district more than an hour before it was due to land.
The remote Nallamalla forest area where it vanished is a stronghold of Maoist rebels in Andhra Pradesh state.
But federal officials have ruled out the possibility that insurgents shot down the helicopter.
Andhra Pradesh is one of a number of Indian states with a significant Maoist rebel presence.
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