An explosion at a remote Sufi Muslim shrine in the Pakistani region of Balochistan has killed 52 people and injured more than 100, officials say.
Emergency services struggled to reach the Shah Noorani shrine in Kuzdar.
Worshippers were performing dhamal - a trance-like dance - when the bomb hit. So-called Islamic State says one of its suicide bombers carried it out.
Sufism, a tolerant, mystical practice of Islam, has millions of followers in Pakistan but is opposed by extremists.
The shrine attracts Sufi devotees from all over the country, as well as neighbouring Iran.
Officials say the bomb blast took place while hundreds of worshippers were present, taking part in the dhamal, which is staged every sunset.
Because the shrine is in rough, hilly terrain, rescue efforts are difficult.
A renowned charity, the Edhi Foundation, says it has sent 50 ambulances which are now carrying people to hospitals in Karachi, 100km (62 miles) away, but officials say they need helicopters to save more lives.
Pakistani Prime Minister Nawaz Sharif condemned the attack and called for speedy rescue efforts.
Imran Khan, former cricketer and head of the Tehreek-e-Insaf party, said the attack had targeted the "core of our society".
The BBC's Charles Haviland says that because Sufism includes music and dance and reverence for saints, religious zealots often target its sites in Pakistan.
In June a famous Sufi singer, Amjad Sabri, was assassinated by two gunmen in Karachi.
Extremist groups in the province of Balochistan have frequently targeted civilians this year.
In October, dozens were killed in an attack on a police college in the city of Quetta and in August an attack on a hospital there killed 70 people.
But doubt has been cast over IS claims of previous attacks in the country.