At least 20 people have been killed in an attack at a Shia mosque in Pakistan.

The blast occurred during Friday prayers at Shikarpur, southern Pakistan, police said.

Another 50 were injured during the blast.

The death toll is expected to rise as many wounded people are in critical condition, police added.

Nobody has yet claimed responsibility for the attack, but suspicions are likely to fall on the Pakistan Taliban, who in December attacked a school in Peshawar, killing hundreds of children.

Pakistan Prime Minister Nawaz Sharif condemned the attack and expressed his condolences to the grieving families.

Meanwhile, Twitter users are expressing outrage and are highlighting a problem of shortage of medical staff and resources in hospitals in Shikarpur.

Speaking to IBTimes UK, Twitter user maaha said the hospital where injured people have been taken "does not have the capacity to take in so many dead bodies and injured people."

"There are no proper hospitals in Shikarpur," she added. "People did the rescue work themselves."