China is holding military exercises in the disputed South China Sea coinciding with US President Joe Biden's visits to South Korea and Japan that are largely focused on countering the perceived threat from Beijing.
The Maritime Safety Administration office in the southern island province of Hainan said the drills began Thursday and would continue through until Monday.
It said other aircraft and vessels will be prohibited from entering the area but gave no further details.
Mr Biden arrived in South Korea on Friday, the first stop on his first trip to Asia as President.
He was due to meet new President Yoon Suk-yeol, a relative newcomer to politics, for the first time in person. The two were to tour a Samsung Electronics plant together ahead of a full day of events on Saturday.
China claims the South China Sea virtually in its entirety and the crucial waterway has become a potential flashpoint for conflict in Asia.
The US does not take a foreign position on the sovereignty issue but insists on the right to operate freely in the sea and frequently sails warships close to militarised Chinese-held islands in the area in what are termed "freedom of navigation operations".
China routinely protests such missions, labelling them deliberate provocations that endanger peace and stability.
To assert its claim, it has built airstrips and other military infrastructure atop human-made islands built on coral reefs and atolls.
Brunei, Malaysia, the Philippines and Taiwan also exercise overlapping claims in the South China Sea.
The Philippine coast guard said on Friday it had established outposts on three islands in the contested waters, a move that will likely be frowned upon by Beijing.
Since the beginning of the month China's first aircraft carrier, the Liaoning, has been conducting a mission in the Sea of Japan, described by the Defence Ministry as "routine training" aimed at boosting performance that is "in-line with relevant international law and international practice, and not targeting any party".
China also flew a pair of long-range nuclear-capable H-6 bombers through the area on Wednesday, Chinese media reports said.
While in Japan, Mr Biden will meet on Tuesday with fellow leaders of the Indo-Pacific strategic alliance known as the Quad, a group that includes Australia, India and Japan.
The four nations share concerns over China's growing regional assertiveness and increasingly capable armed forces.
China views the grouping as a part of a US-led push to impede its economic and political rise and frustrate its attempts to intimidate self-governing Taiwan into accepting its demand to accept Beijing rule.
On Wednesday, Chinese Foreign Minister Wang Yi criticised what he called negative moves by Washington and Tokyo against Beijing during a video call with Japanese Foreign Minister Yoshimasa Hayashi.
"What arouses attention and vigilance is the fact that, even before the American leader has set out for the meeting, the so-called joint Japan-US anti-China rhetoric is already kicking up dust," Mr Wang said, according to China's Foreign Ministry.
Philippines establishes coast guard outposts in disputed sea
Philippines officials in a statement on Friday said the three new coast guard outposts on three islands in the hotly contested Spratly archipelago would monitor ship movements and promote safety, amid increasing maritime tensions with China.
The statement came only days after Philippines president-elect Ferdinand Marcos Jr said his country's ties with China would expand and "shift to a higher gear" when he took power.
China has protested any new constructions in the region although it has transformed seven disputed reefs into military-guarded island bases in past years.
Coast guard Admiral Artemio Abu said the outposts on the islands, which were established this week, would be staffed by coast guard personnel and equipped with radio communications to report any incidents.
Admiral Abu did not specify how many personnel would be stationed at the new outposts but said it was the largest deployment in the disputed region so far.
"Through these command observation posts, we improve our capabilities in promoting maritime safety, maritime search and rescue, and marine environmental protection," he said in a statement.
The three islands have been occupied by Filipino troops for years and are internationally known as West York and Nanshan islands and Northeast Cay.
Last week, the coast guard installed five navigational buoys carrying Philippine flags just off the three islands and near Thitu island, the largest of nine islands and islets Filipino forces have occupied in the Spratlys.
The Philippines considers much of the Spratlys as part of its western Palawan province.
The "sovereign markers" flash lights at night to guide fishermen and ships and "communicate that the said vicinity waters are considered special protected zones" where mining and oil exploration are prohibited to preserve their rich natural resources, Admiral Abu said without elaborating.
China and the Association of South-East Asian Nations, which includes four member states involved in the territorial disputes, have resumed talks this year on a proposed "Code of Conduct," or a non-aggression pact aimed at preventing armed confrontations in the region.
But the negotiations have faced years of delay, partly due to the onset of the coronavirus pandemic in 2020.
AP
