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.

The Al-Khair school is in a narrow street which only one vehicle can pass through at a time - meaning it was difficult for rescue workers to reach the site and transport the injured to hospitals.

Peshawar's Lady Reading Hospital reported 32 children and a teacher dead while Naseerullah Khan Babar Memorial Hospital reported one child dead.

An English teacher from a nearby school said he immediately rushed to the site with other local residents when he heard sirens and the sound of ambulances.

Together, they pulled out more than 20 children from the rubble, he said.

"I personally pulled out six children with my own hands. Most of them were alive and talking. But later it was found that they had passed away."

"There was a lot of blood," he said. "One child said he was in a lot of pain. His tongue had dried up in his mouth, [and he was] asking for water."

Sohail, another local resident, said he and others tried to pull children from under the rubble "using shovels".

Police chief Mian Saeed said the building was still "extremely dangerous" and urged people to move away.

"This is a case of gross negligence," he said. "We will examine whether there were any violations of building codes. We intend to conduct a thorough inquiry and gather all the facts."

Saeed confirmed the school's owner had been arrested.

The governor of Khyber Pakhtunkhwa, Faisal Karim Kundi, has also ordered a safety audit of all schools in the province to "identify potential risks and ensure that immediate corrective measures are taken wherever necessary".

"We cannot allow the safety of our children to be compromised," he said.

Four months ago, fourteen children died after the roof of a private tuition centre near Lahore collapsed.

And in August, 14 newborn babies were killed by a fire that ripped through a neonatal unit at a hospital in the capital, Islamabad, which an inquiry found lacked fire alarms and sprinklers.