Phnom Penh, Jun 24 (IANS): The death toll in the collapse of a seven-storey under-construction building in Cambodia's Preah Sihanouk province has increased to 24, according to authorities on Monday.

"As of 6.30 a.m. on Monday, 24 people were found dead under the debris, and 24 others were injured," Xinhua news agency quoted the authorities as saying, adding that the rescue operation is still going on.

Prime Minister Hun Sen headed to Sihanoukville on Sunday evening to oversee the rescue operation, according to a post on his Facebook page.

Preah Sihanouk Provincial Governor Yun Min told Xinhua that it was believed that between 40 and 50 construction workers were asleep in the building when it collapsed on Saturday morning.

Seng Loth, a spokesman for the Ministry of Land Management, Urban Planning, and Construction, said the building was constructed without permission.

"It was an unlicensed project, and the provincial authorities had warned the developer twice, but they ignored the warnings," he told Xinhua.

He said an investigation has been launched into the cause of the collapse.