Modi had started to extol his government's achievements when the tent's canopy fell onto the crowd amid heavy rain, seriously injuring two people.
"The incident happened about 100 metres from the dais as the prime minister began to address the rally," senior state police official Anuj Sharma said.
"The prime minister paused and urged the people to stay calm."
Television footage showed injured audience members being lifted to safety by the public.
Samir Dash, the district chief of Modi's Bharatiya Janata Party, said the tent collapsed because people tried to climb up the bamboo poles holding the tent aloft.
Modi later visited the local hospital to check on the injured.
One woman brought to the ward from the rally asked for the premier's autograph as she lay in bed.
Modi is set to address a slew of public rallies in the coming months ahead of general elections next year.
Last modified on Tuesday, 17 July 2018