At least 36 people were killed and more than 50 injured on Saturday at a rally held by Tamil actor Vijay, who is campaigning for election, state officials said.
"Thirty-one people died with more than 50 people now hospitalised," said V. Selvaraj, a senior police official in the district of Karur in Tamil Nadu, where the incident occurred.
Large crowds had gathered for the meeting, part of Vijay's ongoing state tour for his political party Tamilaga Vettri Kazhagam.
At least 44 doctors from the nearby districts of Tiruchirappalli and Salem were sent to Karur, media reports said.
Vijay, who is a well-known actor and goes by only one name, launched a political party last year and began campaigning this month ahead of state elections that are to be held early next year.
State lawmaker Senthil Balaji told reporters that 58 people were hospitalised after what he said was a stampede.
He added that Tamil Nadu Chief Minister MK Stalin will visit the area on Sunday.
"The news coming from Karur is worrying," Stalin said in an X post, adding that he had directed ministers and officials to provide urgent medical aid to those who collapsed at the Karur rally and ordered additional assistance from nearby Tiruchirappalli.
In a statement issued late Saturday night, the Chief Minister conveyed his heartfelt condolences to the families of those who lost their lives.
"This is an unprecedented tragedy. My deepest sympathies are with the bereaved families. The government stands by them in this painful moment," Stalin said.
Announcing immediate relief, the Chief Minister declared an ex gratia of Rs10 lakh (Rs1 million) from the Chief Minister's Public Relief Fund to the families of each deceased person.
Those seriously injured and undergoing treatment at various hospitals will receive Rs100,000 each. Stalin directed that all medical expenses for the injured be fully covered by the government.
President Droupadi Murmu has expressed deep anguish over the "loss of lives" in a stampede during Tamilaga Vetri Kazhagam (TVK) chief Vijay's rally at Karur in Tamil Nadu
"Anguished to know about the tragic loss of lives in a stampede-like unfortunate incident in Karur district of Tamil Nadu. I extend my deepest condolences to the bereaved family members and pray for early recovery of those injured," President Murmu said in a post on X late Saturday.
Tamil Nadu Governor RN Ravi also conveyed his grief, describing the loss of innocent lives, including children, as "deeply pained and anguished."
In a statement, he said, "My heartfelt condolences to the bereaved families in this time of grief and prayers for the speedy recovery of those injured."
"The unfortunate incident during a political rally in Karur, Tamil Nadu, is deeply saddening," Prime Minister Narendra Modi said in a post on X.
Modi expressed his grief over the tragedy, saying, "My thoughts are with the families who have lost their loved ones. Wishing strength to them in this difficult time and praying for a swift recovery to all those injured."
Defence Minister Rajnath Singh, describing the tragedy as "heartbreaking," offered his condolences and wished the injured a quick recovery.
Agencies