Malaysian Prime Minister Mahathir Mohamad on Thursday warned the Philippines against letting in foreigners who could "disturb" the country's domestic political stability, as President Rodrigo Duterte's Beijing pivot sparks an influx of Chinese workers.
At least 200,000 Chinese have flocked to Manila since Duterte's 2016 election, many of them employed by online gaming firms that cater to Chinese players, a Philippine Senate inquiry was told late last year.
Some Filipino politicians have alleged this drives up property prices, takes away jobs from locals and even affects tax revenues.
Mahathir, who has suspended several of his nation's major projects with China, warned during an official visit to the Philippines against allowing a surge of foreigners.
"Foreign direct investment should not involve bringing huge numbers of foreigners to live in the country, because that might disturb the political equations in the country," Mahathir told ABS-CBN television in an interview.
"If huge numbers of any foreigners (come) to live and stay in the country... you have to do some rethinking as to whether it is good or bad, or the limits that you have to impose on them," Mahathir said.
Mahathir, 93, is in the Philippines for the first time since his shock election victory last year. He held talks with Duterte and addressed a business forum after the television interview.
The Malaysian leader has taken a cautious approach to relations with China, saying he would discuss "unfair" terms of deals signed by his predecessor, Najib Razak.
Duterte's pursuit of closer ties with China for the Philippines -- a traditional ally of the United States -- has prompted a surge of Chinese worker arrivals.
Last year legislators said around 200,000 Chinese were working in the country, and vowed to introduce protection for Filipinos.
Philippine Finance Secretary Carlos Dominguez had also said he would ensure that foreigners working in the nation's offshore gaming industry paid taxes.
But Duterte last month said Chinese workers should be allowed to continue staying in the country as Beijing also hosted hundreds of thousands of Filipinos. Most of them are domestic workers in Hong Kong.
Duterte has warmly embraced China despite his nation's long-standing maritime row with Beijing over the South China Sea.
Beijing asserts sovereignty over almost all of the resource-rich sea, with competing claims from the Philippines, Malaysia and other nations.
Commenting on the sea dispute on Thursday, Mahathir said there should be no impediment to vessels using the strategic waterway, through which trillions of dollars in global trade pass each year.
"The South China Sea in particular must be open to navigation," he said in the television interview.
- Peace process -
At their meeting, Mahathir and Duterte hailed a peace process that put leaders of the Philippines' largest Muslim guerrilla group at the helm of a new self-governing area near the mainly Catholic nation's sea border with Malaysia.
The decades-old rebellion in the Mindanao region claimed 150,000 lives, ushered in violent extremist groups and caused tens of thousands of Filipinos to flee to Malaysia to escape the violence and find work.
Duterte said he thanked Mahathir for Malaysia's "unrelenting support for development in the south" and playing a key role in the peace process, which included helping monitor a ceasefire and hosting formal negotiations.
Mahathir said he assured Duterte "of Malaysia's desire to... address the serious issue of terrorism and violent extremism".