The bombing of the famed Lal Shahbaz Qalandar shrine in Sindh province was Pakistan's deadliest attack in two years and capped a wave of violence this week that underlined the ongoing ability of militant groups like the Pakistani Taliban and Islamic State to cause havoc.

An offshoot of the Middle East-based Islamic State said it was responsible for the bombing, the second major attack on a Sufi shrine in three months.

The white marble floor at Lal Shahbaz Qalandar was still marked by blood on Friday, and a pile of abandoned shoes and slippers was heaped in the courtyard, many of them belonging to victims.

Outside, protesters shouted slogans at police, who they said had failed to protect the shrine.

"I wish I could have been here and died in the blast last night," a devastated Ali Hussain told Reuters, sitting on the floor of the shrine.

He said that local Sufis had asked for better security after a separate bombing this week had killed 13 people in the eastern city of Lahore, but added: "No one bothered to secure this place".

Anwer Ali, 25, rushed to the shrine after he heard the explosion, and described seeing dead bodies and chaos as people fled the scene.

"There were threats to the shrine. The Taliban had warned that they will attack here, but authorities didn't take it seriously," Ali said.

A wave of bombings over five days has hit all four of Pakistan's provinces and two major cities, killing nearly 100 people and shaking a nascent sense that the worst of the country's militant violence may be in the past.

Most of the other attacks have been claimed by factions of the Pakistani Taliban, which is waging its own fight against the Pakistani government but whose ranks have also cooperated with and sometimes defected to Islamic State.

In the past two years, Islamic State has worked to build its "Khorasan province" encompassing Afghanistan and Pakistan.

Islamic State media outlets have claimed several major attack in Pakistan, including one on another shrine in southwestern Baluchistan province that killed at least 52 people last November.

The month before, the group said it had carried out an assault on a police training college in the same province, killing at least 59 people.