A major rescue operation is under way to save dozens of people thought to be trapped in rubble after a factory collapsed in Lahore, Pakistan.

At least 17 people died when the factory, which was under construction, collapsed on Wednesday.

Cranes and bulldozers are being used and the army is assisting in the rescue efforts.

The cause of the collapse is still unknown. Building safety levels are often below standard in Pakistan.

Two floors of the factory, in the Sundar Industrial Estate on the outskirts of the city, were operational, while a third was being built.

About 200 labourers are thought to have been in the building at the time of the incident, according to Jam Sajjad Hussain, a spokesman for the rescue services.

Other estimates in the Pakistani media have put the figure closer to 150 people.

Hussain told the BBC that 98 people had been pulled out alive and many were then taken to hospital.

He said it was difficult to know exactly how many people were still trapped because the owner and administrative employees were among those inside the building.

The army has said that it is deploying a team of engineers and experts to take part in the rescue.

In September last year at least 24 people were killed in Lahore when the roof of a mosque collapsed.

At least 17 people - including children - were killed in a factory collapse following a gas explosion in a residential area of the city in February 2012.