As many as 28 people, including 18 children, were killed at an elementary school in Newtown, Connecticut, about 60 miles northeast of New York Friday.
The shooting appeared to be the nation's second-deadliest school shooting, exceeded only by the Virginia Tech massacre in 2007, in which 32 people, including two Indians, were killed and 17 others wounded.
Here's what the celebrities tweeted:
Shruti Haasan: So sad and disturbed this morning to hear about the shooting in Connecticut, little kids. This is just so sad, prayers to their families.
Shekhar Kapur: Heart goes out to parents and families of children who died in Connecticut.
Karan Johar: Shocked and appalled at the massacre in Connecticut. Prayers to the families who bear this tragic loss and Proactivity to America.
Kunal Kohli: If guns are sold they will be used. Too many times have too many innocents died. The gun lobby still think they're living in the Wild West? The US has to relook and change their gun laws. These killings have to stop. It's sad meaningless and ridiculous. Guns can't be sold to anyone.
Sanjay Gupta: What can be more ridiculous than this statistic? US has more retail gun stores 51, 438 than grocery stores 36, 569.
Neha Dhupia: Its unimaginable to see what's happened in Newtown, Connecticut. Strength to each one who has lost their loved ones.
Amitabh Bachchan: Atrocious! Saddened beyond grief! Just cannot believe that a human can possess such a sick demented mind! Prayers for families. Gun control? Try getting it passed in the Senate - it shall be gunned down.
Manoj Bajpayee: Sad news from US, it is atrocious that guns are so comfortably available to a 20-year-old. My heart goes out to those who lost their little ones.
Farhan Akhtar: Deepest sympathies to the families of all the innocent lives lost in Connecticut. Our thoughts are with you.
Ehsaan Noorani: Gun control is the need of the hour. Each little soul cries out.
Ritesh Sidhwani: Shocked and Saddened to hear about the shooting in a Elementary school in Connecticut. What is this world coming to. My heart goes out to the grieving parents of the little angels.
Kabir Khan: How many school kids will be gunned down before the US begins gun regulation? It's like their foreign policy - the wrong guys are given guns.
Jackky Bhagnani: Shameful at what happened at Connecticut. A complete inhuman act. Prayers for all the children who ended their life before even starting it.
Farah Khan Ali: A society that attacks innocent children is a doomed society wherever and whichever country it maybe. Children are reflection of God.