China is the largest investor in Cambodia and has pumped billions into the economy while asking few questions about its abysmal rights record.

While doling out cash China has also sought high-profile military exchanges, fuelling speculation that it is building a naval base off the Cambodian coast, claims vehemently denied by Prime Minister Hun Sen.

Several joint military exercises have also taken place while in June Beijing promised $100 million to modernise Cambodia's armed forces.

The three warships, the longest 180 metres (590 feet), stopped at Cambodia's Sihanoukville port for a visit to January 12, Cambodian defence ministry spokesman Chhum Socheat told AFP.

"The goal of the visit is to boost ties and military cooperation, especially between the navies from both countries," he said, dismissing suggestions that the display was about touting "Chinese influence".

He said the Chinese navy delegate would meet with Cambodian military commanders and Defence Minister Tea Banh during the visit.

Rumours that China has been building ae base off Cambodia's southwest coast have been swirling for years but reached new levels after Hun Sen said US President Vice President Mike Pence sent him a letter about it in November.

The strongman leader, who has been in power for more than three decades, said Cambodia would not allow foreign military bases on its soil.

In return for its longstanding support Cambodia has proved a reliable ally among the ASEAN Southeast Asian bloc regarding disputes with China over its activities in the South China Sea.

Beijing's claims in the waterway have angered the Philippines, Vietnam and Malaysia who all have competing claims to its islands and potentially resource-rich waters.

China has also backed Cambodia on sensitive issues, including a controversial election in July held without the opposition.

The mutual support comes as US influence declines.

Cambodia accused the US of conspiring with an opposition leader to overthrow the government and suspended military exchanges with the country.

But while Chinese-bankrolled developments may have fanned growth they risk incubating resentment among some Cambodians who fear the country is increasingly in the pocket of the regional superpower.