Karachi: A powerful bomb ripped through a packed Sufi shrine in southern Pakistan on Thursday night, killing nearly 100 people and injuring dozens of others, prompting the government to clamp emergency measures.

The attack took place at the revered Sufi Lal Shahbaz Qalandar shrine in Sehwan town, some 200 km northeast of the port city of Karachi.

The dreaded Islamic State group has claimed responsibility for the attack.

The authorities have immediately launched a massive rescue and relief operations even as the toll rose to nearly 100, media reports said.

The bomber entered the shrine through its Golden gate and blew himself up near the site where the ritual of sufi dance 'Dhamal' was taking place, PTI quoted SSP Jamshoro Tariq Wilayat as saying.

The attacker first threw a grenade, which failed to explode, the officer added.

Sehwan police station SHO Rasool Baksh told reporters that around 100 people, including women and children, have been killed in the suicide attack.

Hundreds of devotees were present inside the premises of the vast mausoleum of the saint at the time of blast.

Faisal Edhi of the Edhi foundation confirmed they have shifted 60 bodies to hospitals in Hyderabad and Jamshoro.

The ISIS claimed responsibility for the attack on their Aamaq news agency, saying a suicide bomber had targeted a "Shiite gathering" at the shrine in Sindh.

Commissioner Hyderabad Kazi Shahid said since the shrine was located in a remote area, some 130 kms from Hyderabad, ambulances and vehicles and medical teams were being sent from Hyderabad, Jamshoro, Moro, Dadu and Nawabshah to the blast site to take care of the injured and move the bodies.

"Emergency has been declared at hospitals in these places and rescue operations have started," he said.

Sindh Chief Minister Syed Murad Ali Shah said that the Pakistan army had been requested to provide night flying helicopters to shift the dead and injured.

"Yes it is a tragic incident and because the shrine is away from a major city there have been problems in providing rescue operations," he said.

The army said a C130 aircraft will be used to lift the injured from Nawabshah.

Prime Minister Nawaz Sharif condemned the attack and urged Pakistan to "stand united".

Devotees gather at the shrine of the revered Sufi saint every Thursday to participate in a dhamaal and prayers.

Television channels reported that dead bodies and injured were lying inside the shrine of Lal Shahbaz Qalandar, a Sufi philosopher-poet of present-day Afghanistan and Pakistan.

(With Agency inputs)