Rodrigo Duterte, aiming to attract trade and investment from China, has up until now mostly withheld his early criticism of China's expansive claims to the sea.
Philippine President Rodrigo Duterte voiced rare frustration with China, urging progress on a code of conduct for the contested South China Sea, which he warned was becoming a "flashpoint".
Duterte was delivering a speech at an economic forum in Tokyo, but veered off script with remarks about the resource-rich sea, over most of which China claims sovereignty despite competing claims from the Philippines, Malaysia, Brunei, Taiwan and Vietnam.
"I love China... but it behooves upon us to ask, 'is it right for a country to claim the whole ocean?" he said.
Beijing and the 10-member Association of Southeast Asian Nations (ASEAN) have for years tried to hammer out a code of conduct to govern the disputed waters, but the process has been slow.
"I am sad and bewildered -- not angry, because I cannot do anything," Duterte said. "I just hope China will come up with this 'conduct' soon.
"The longer it takes," he said, the greater the chance the sea would be a "flashpoint of troubles", adding that France, Britain, and the United States are already "testing the waters".
Duterte, aiming to attract trade and investment from the Asian superpower, has mostly withheld his early criticism of Beijing's expansive claims to the sea -- a point of regional contention because trillions of dollars of goods pass through it.
But in April he warned Beijing to back off from a disputed island in the sea, suggesting the possibility of military action if China touched it.
In a major victory for Manila, an international maritime tribunal ruled early in Duterte's presidency that China's claims to the area have no legal basis.
However, he has largely set aside that ruling and backed off on their once tense territorial dispute over the sea, prompting criticism at home that he has been soft on China.
"China says, 'this is our land, this is our sea. Anyone who goes in there will just have to contend with us. Maybe with arms'," Duterte told the Future of Asia forum.
"My country is very small. I cannot afford to go to war with anybody, not only with China."
Duterte also voiced worries about the escalating trade war between Beijing and Washington, saying it could only harm the world economy.
"It is creating uncertainty and tension," he said.