PHNOM PENH (Reuters) - Up to 50 Chinese nationals have been detained in Cambodia as part of a crackdown on prostitution rings in Sihanoukville province, a Chinese investment hub, the provincial governor said on Tuesday.

Cambodian Prime Minister Hun Sen is a close ally of Beijing and the Southeast Asian country has attracted a surge of Chinese investment in the capital, Phnom Penh, and cities like Sihanoukville, where the development of casinos and hotels has expanded rapidly.

Sihanoukville, a coastal city 225 km (140 miles) west of Phnom Penh, has seen a construction boom in recent years supported by a steady stream of Chinese money.

However, the influx of Chinese workers and money has also stirred local resentment and what some authorities say is a rise in criminality in the once-sleepy port town.

Governor Yun Min said Chinese investment in the province had topped $1 billion but the money came with a rise in illegal sex services provided by and for Chinese nationals in the area.

“When a lot of them come, there are also a lot of demands for the service,” Yun Min told Reuters.

“It is illegal in our country so we have to stop it and crack down,” he said. “The crackdown will continue indefinitely.”

China’s embassy in Phnom Penh did not respond to an emailed request for comment.

Sihanoukville police chief Phul Phorsda said the crackdown was continuing but declined to comment further.

A police report obtained by Reuters said police had confiscated leaflets offering sex services, featuring naked women and phone numbers, during raids at massage parlors.

China’s support allowed Hun Sen to defy Western criticism of a crackdown on his opponents in the lead-up to a general election last month in which his ruling Cambodian People’s Party (CPP) said it won all 125 parliamentary seats.

Official election results are expected on Wednesday.

The opposition Cambodia National Rescue Party was dissolved by a court last year at the request of Hun Sen’s government, prompting condemnation from several Western countries.

Yun Min, who complained in a letter to the interior minister in January that the Chinese influx had pushed up crime in Sihanoukville, downplayed his earlier comments on Tuesday, saying that Chinese investment was positive on the whole.

“China has a lot of other good citizens, the 50 people in detention don’t represent the whole Chinese population,” he said.