More than 20 Chinese nationals have gone missing after a boat capsized off the coast of Cambodia.

"A boat carrying 41 Chinese nationals ran into difficulties near Sihanoukville on Thursday, and only 18 people on board have been rescued," provincial spokesman Khiang Pharom said, according to French news agency AFP.

The village of Sihanoukville has been transformed rapidly in recent years by Chinese investment, with dozens of casinos opening up.

Cases of Chinese workers being illegally trafficked to work in the city are on the rise.

"Police are interrogating the people they rescued, while the search for others is ongoing," provincial spokesman Khiang Phirom said.

"We are looking for 23 missing people," he said.

A representative of the group told police that they left by speedboat from a port in China's Guangdong province on September 11, provincial police chief Choon Narain told pro-government media outlet Fresh News.

"About a week later, they were transferred to international waters in a wooden boat with two Cambodian crew members, which broke down on Thursday and began to sink," the police chief said.

"A fishing boat picked up the two Cambodians and left them and their boat in the sea," he said.

The two Cambodian nationals have also been taken into custody for questioning, according to provincial spokesman Khiang Phirom.