At least 24 people now known to have died after construction workers were trapped inside building when it collapsed.

At least 24 people have died and 23 were injured after a building under construction in Cambodia collapsed, trapping workers beneath the rubble, officials said on Sunday.

The seven-storey concrete building collapsed on Friday in the coastal town of Kep, about 160 kilometres (100 miles) southwest of the capital Phnom Penh, the latest collapse to hit the country's booming construction industry.

"Twenty-four people have died so far," Kep Governor Ken Satha told Reuters News Agency. "Three of the bodies are not yet at hospital, they have not been pulled out yet."

There are an estimated 200,000 construction workers in Cambodia, most of them unskilled, reliant on day wages and without union protection, according to the International Labour Organization.

Worker advocates point to low standards at construction sites that increase the risk of accidents.

Labourers can often be seen shirtless, working with little protective gear, and sleeping inside partially-completed buildings.