An explosion took place at a mosque, where a large number of people had gathered for prayer, in the northwestern city of Peshawar in Pakistan on Monday, a police official told Reuters.

"A portion of the building had collapsed and several people are believed to be under it," police official Sikandar Khan said.

Mohammad Asim, a spokesman for the Lady Reading Hospital in Peshawar, said they had received 70 injured, some of them in critical condition. (Reporting by Jibran Ahmed in Peshawar, writing by Shilpa Jamkhandikar; editing by Sudipto Ganguly)