Dozens of guests had assembled for the ceremony outside a family home in the western state of Rajasthan when the transformer exploded.
Dozens of guests had assembled for the ceremony outside a family home in the western state of Rajasthan when the transformer exploded, spewing hot oil and metal shards.
"Four people died on the spot," local police superintendent Rameshwar Singh told AFP.
"We are ascertaining the cause of the blast."
Singh said several others were being treated for severe burns after the disaster, which triggered protests against the electricity department.
Locals said they had raised concerns about the maintainance of the transformer with officials, but nothing had been done.
They also said a circuit-breaker failed to work after the blast, exacerbating the disaster as live wires fell onto the crowd late Tuesday in the state capital Jaipur.
Transformers are part of the electricity distribution system and help maintain a uniform current.
India's power distribution system is prone to accidents, mostly because of poor maintainance and underfunding in rural areas.
Nearly 10,000 people died due to electrocution in India in 2015, according to the most recent data available from the national crimes records bureau.
Rajasthan chief minister Vasundhara Raje has ordered a high-level inquiry into the incident.