At least 33 pupils and a teacher have been killed after a school roof collapsed in the north-western Pakistani city of Peshawar, according to hospital officials.

More than a dozen others are injured, with some in a critical condition. Several children are feared to be trapped under the rubble.

Emergency services were alerted to the incident at the private Al-Khair school in Dir Colony at 08:48 (03:48 GMT) on Thursday after lessons had begun, a rescue official said.

He told the BBC the roof of an upper-floor classroom had collapsed, causing ceilings below to cave in as well.

Warning: This article contains distressing details

"The children in the affected [classrooms] were trapped under the debris," the official, Bilal Faizi, said.

The school is located in a building that had been constructed on a temporary basis, according to emergency official Arif Khattak.

Earlier reports suggested the affected classrooms were in a two-storey part of the building, but Peshawar police chief Mian Saeed later confirmed that classrooms on three floors had been brought down. There were about 30 pupils in the top class, 40 in the middle and 45 on the ground floor, he said.

It appears that when the roof of the upper-floor classroom collapsed, the falling rubble crashed through classrooms below, bringing their ceilings down too.

Saeed said the entire structure, which had "substandard" roof slabs, was "overloaded" and beyond the limit of how much weight it could bear.