Police officers were among the 33 killed and 150 wounded in a blast at a mosque inside a highly sensitive Pakistani police headquarters on Monday, prompting the government to put the country on high alert.

The attack happened during afternoon worship in the provincial capital of Peshawar, close to former tribal areas that border Afghanistan where militancy has been steadily rising.

A frantic rescue mission was underway at the mosque, which had an entire wall and some of its roof blown out by the force of the blast.

"Many policemen are buried under the rubble," said Peshawar police chief Muhammad Ijaz Khan, who estimated between 300 and 400 officers usually attended prayers at the mosque.

"Efforts are being made to get them out safely," he said.

Bloodied survivors emerged limping from the wreckage, while bodies were ferried away in ambulances as the rescue operation continued.

"It's an emergency situation," Muhammad Asim Khan, a spokesman for the main hospital in Peshawar told AFP, putting the death toll at 33.

Khyber Pakhtunkhwa governor Ghulam Ali put the death toll at 28 and 150 wounded, most of them policemen.

The police headquarters in Peshawar is in one of the most tightly controlled areas of the city, housing intelligence and counter-terrorism bureaus, and is next door to the regional secretariat.

The country was put on high alert after the blast, with checkpoints ramped up and extra security forces deployed, while in the capital Islamabad snipers were deployed on buildings and at city entrance points.

"Terrorists want to create fear by targeting those who perform the duty of defending Pakistan," said Prime Minister Shehbaz Sharif in a statement.

"Those fighting against Pakistan will be wiped out from the face of earth."

- 'Black smoke rising' -

Officers said the blast came from the second row of worshippers, with bomb disposal teams probing the possibility of a suicide attack.

Shahid Ali, a policeman who survived, said the explosion took place seconds after the imam started prayers.

"I saw black smoke rising to the sky. I ran out to save my life," the 47-year-old told AFP.

"The screams of the people are still echoing in my mind," he added. "People were screaming for help."

The drastic security breach came on the day United Arab Emirates (UAE) President Mohamed bin Zayed Al Nahyan had been due to visit Islamabad, although the trip was cancelled at the last minute due to bad weather.

Pakistan is also preparing to host an International Monetary Fund (IMF) delegation on Tuesday as it works towards unlocking a vital bailout loan to prevent a looming default.

- History of violence -

The security situation in Pakistan –- once plagued by bombings until a major military crackdown that began in 2014 largely restored order –- has deteriorated since the return of the Afghan Taliban in Kabul.

Islamabad has accused the new rulers of failing to secure their mountainous border, allowing militants to travel back and forth without being detected.

The biggest threat comes from a resurgent Pakistani Taliban, a separate movement from the Afghan Taliban but with a similar ideology, which has sharply increased low casualty attacks on police and security forces.

Meanwhile, the regional chapter of the Islamic State –- whose numbers were bolstered by prison breaks in Afghanistan in 2021 –- claimed an attack on a minority Shiite mosque in Peshawar that killed 64, Pakistan's deadliest terror attack since 2018.

Detectives said the bomber was an Afghan exile who had returned home to train for the attack.