Some 5,000 rescue workers battled through the night to contain the blazes in the Khakassia region of southeastern Siberia, where 23 people died, said investigators.
Fires also raged in eastern Siberia, claiming three lives including that of a three-year-old girl, authorities in the Chita region told AFP.
The Kremlin said President Vladimir Putin was personally coordinating the emergency response.
The authorities blamed the fire on human carelessness, with people suspected of setting dry grass alight and strong winds and warm temperatures then causing the fire to spread.
More From This Section
"And it was adults and not children who did this."
State television said the fires were so intense they could be seen from space, on satellite images, and that the flames reached about three meters in some places.
A senior medical official, Natalya Kogan, told reporters that more than 900 people sought medical help in Khakassia.
A total of 77 people were hospitalised, a spokeswoman for regional authorities, Irina Emelianova, told AFP earlier in the day.
"We have never had this before," Emelianova said, referring to the scale of the disaster.
More than 30 villages have been affected, she added. Some 5,000 people had been left homeless, including 1,000 children.
Regional authorities reported large livestock losses as a result of the blaze.
At least 700 cattle and some 3,000 sheep had perished, they said in a statement, expressing concern that surviving cattle had no grass to graze. "Tens of square kilometres of land have been burned," they added in a statement.
Moscow-based investigators have opened five criminal probes into the Khakassia fires.