Narendra Modi said he was praying for the swift recovery of ten people who were injured in the incident.
The guests were killed when a concrete slab they were dancing on gave way, collapsing into a disused well in the northern Indian state of Uttar Pradesh on Wednesday.
An official said the victims were singing and dancing at a ceremony when the slab gave way.
Those injured and taken to hospital in Kushinagar district.
Rescue worker Muralidhar Singh said the well was more than 50ft (15-metres) deep.
The incident took place during a traditional “haldi” ceremony, in which turmeric paste, oil and water are applied to the faces of the bride and groom to bless the couple before the wedding.
Police said 11 people were declared dead immediately, two others died later during treatment.
Uttar Pradesh chief minister Yogi Adityanath has asked district authorities to assist the families of the victims.
Authorities said they were investigating the circumstances around the deaths.
