Rescuers have pulled two survivors from the rubble of a building two days after it collapsed while under construction in a Cambodian beach town.

Key points: The two rescued workers are in a "serious condition" in hospital

The two rescued workers are in a "serious condition" in hospital Two senior officials have lost their jobs over the building collapse

Two senior officials have lost their jobs over the building collapse The accident has raised questions about construction standards in Cambodia

At least 28 workers were killed and 26 others injured as they slept in the unfinished condominium that was doubling as their housing in the coastal town of Sihanoukville, west of the capital Phnom Penh.

Seven people, including five Chinese nationals, were charged on Tuesday with involuntary manslaughter and conspiracy over the building collapse.

Preah Sihanouk provincial authorities said rescuers digging through the twisted metal and concrete rubble found two survivors and four bodies on Monday.

The steel structure collapsed in on itself, which has stymied rescue efforts. ( AP: Heng Sinith )

A hospital official, speaking on condition of anonymity as he was not authorised to comment to the media, said the two survivors were very weak and could only talk in a soft voice.

"They are in serious condition after being trapped since early Saturday without any food or water," he said.

Investigators are trying to determine what caused the seven-storey steel and concrete structure to crumple without warning before dawn, trapping construction workers who were sleeping on the site.

Seaside investment boom

The port and resort town has seen a rush of Chinese investment in recent years, especially in the casino, property and tourism sectors, and questions have been raised about construction standards.

Prosecutors have charged two Chinese nationals — building owner Chen Kun and construction supervisor Deng Xing Gui — with involuntary manslaughter, causing unintentional injuries and damage, according to the Preah Sihanouk Provincial Court.

Three other Chinese nationals, a Vietnamese and a Cambodian were charged with conspiracy related to the charges, court documents show.

At least 28 workers were killed and 26 others were injured in the incident. ( AP: Heng Sinith )

The men were not available for comment.

Prime Minister Hun Sen fired a top disaster management official for failing to take responsibility for the disaster and accepted the resignation of Yun Min, the Governor of Preah Sihanouk province.

High-level resignations over wrongdoing are rare in Cambodia.

The accident has sparked a public debate about the nature of Chinese businesses in Cambodia, which critics say are allowed to operate without enough scrutiny.

Sihanoukville is home to Cambodia's largest port and a Chinese Special Economic Zone linked to Beijing's Belt and Road initiative.

AP/Reuters