Pakistan on Thursday mourned the 47 victims of its deadliest plane crash in four years, among them two infants and three foreigners, as officials sought to pinpoint the cause of the disaster.

Engine trouble was initially believed responsible, but many questions remain, stirring new worries about the safety record of money-losing state carrier Pakistani International Airlines.

The ATR-42 aircraft involved in the crash had undergone regular maintenance, including an "A-check" certification in October, airline chairman Muhammad Azam Saigol said.

"I want to make it clear that it was a perfectly sound aircraft," Saigol said, ruling out technical or human error.

The aircraft appeared to have suffered a failure in one of its two turboprop engines just before the crash, he said, but this would have to be confirmed by an investigation.

"I think there was no technical error or human error," he told a news conference late on Wednesday. "Obviously there will be a proper investigation."

Outpourings of grief erupted online soon after flight PK661 smashed into the side of a mountain near the town of Havelian late on Wednesday, after taking off from the mountain resort of Chitral.

Foreigners among dead

The foreigners included two Austrians and a Chinese man, the airline said.

The Chinese embassy in Pakistan has verified the Chinese victim's identity and is giving support to his family, Foreign Ministry spokesperson Lu Kang said in Beijing.

Foreign tourists increasingly flock to Chitral every year, besides thousands of domestic visitors, as Pakistan emerges from years of violence caused by a Taliban insurgency.

The aircraft, made by French company ATR in 2007, had racked up 18,739 flight hours since joining PIA's fleet that year. Its captain, Saleh Janjua, had logged more than 12,000 flight hours over his career, the airline said.