"May Almighty give strength to the bereaved families to overcome the grief," Modi tweeted.
"I hope the injured recover quickly. I pray for the safety and well-being of all saints, pilgrims and tourists at the Kumbh."
Tragedy struck the Ardh Kumbh Mela in Ujjain as winds and heavy rain destroyed temporary structures built for tens of thousands of devotees in the Madhya Pradesh city.
One woman was confirmed dead while 20 to 25 people were injured, an official said. At least three of the injured were serious. Some people were also feared trapped under the collapsed tents.