Xi arrived after visiting Vietnam and Malaysia as Beijing seeks to strengthen regional trade ties and offset the impact of huge tariffs imposed by his US counterpart Donald Trump.

The Chinese leader touched down in Phnom Penh on Thursday, where he was greeted by King Norodom Sihamoni during a military welcome ceremony.

Xi will go to the palace on Thursday afternoon before holding meetings with former leader Hun Sen and his son, Prime Minister Hun Manet, according to an official schedule seen by AFP.

In an article by Xi published by Cambodian state-run Fresh News on Thursday, he said China supported the kingdom "choosing a development path that suits the nation, safeguarding its national sovereignty, independence and territorial integrity".

He said the two countries should "resolutely oppose external forces interfering in internal affairs, sowing discord and undermining" relations.

China is Cambodia's biggest trading partner and source of investment, and more than a third of Cambodia's $11 billion in foreign debt is owed to China, according to the International Monetary Fund.

Phnom Penh is among Beijing's most reliable supporters in Asia -- Hun Manet on Wednesday described Xi's visit as a display of "iron-clad" friendship.

In a video posted on Wednesday he said the two countries had "common interests based on the principles of respect for sovereignty, equality, and non-interference in internal affairs".

He also said China had played a "pivotal role" in Cambodia's socioeconomic development.

China and Cambodia this year celebrate 67 years of diplomatic relations and on Thursday the kingdom also commemorated 50 years since the fall of Phnom Penh to the Khmer Rouge.

Earlier this month Trump announced tariffs of 49 percent on Cambodia -- among the highest of his sweeping import duties.

He then paused the levies for most countries for 90 days, reverting to the base tariff of 10 percent.

Hun Manet wrote a letter to Washington "expressing Cambodia's good faith to negotiate a mutual solution" and pledging to reduce its own tariffs on 19 categories of US goods, according to the commerce ministry.

Excluded from the 90-day pause is China, which faces new US levies of up to 145 percent on many products.

Beijing has called the taxes a "joke" and imposed retaliatory tariffs of 125 percent on US goods.