While restraint remains the order of the day, recent developments suggest that rival nations’ maritime “red lines” are hardening.
At the 2025 Munich Security Conference, former Chinese Vice Foreign Minister Fu Ying explicitly described Philippine efforts to occupy Second Thomas Shoal and Sabina Shoal as a violation of the 2002 Declaration on the Conduct of Parties (DOC), calling the seizure of “new rocks” a Chinese “red line no one should be allowed to cross” (emphasis added). She simultaneously implied that China was exercising restraint by not taking such features itself despite possessing the capability to do so.
China’s behavior in the South China Sea illustrates how these thresholds are articulated and enforced in practice. Beijing consistently frames the “new occupation” of previously uninhabited maritime features as unacceptable, invoking the DOC. This position has hardened from diplomatic rhetoric into operational justification.
This logic has been operationalized in increasingly forceful encounters. On June 17, 2024, China Coast Guard vessels blocked a routine Philippine resupply mission to the grounded BRP Sierra Madre at Second Thomas Shoal. Chinese vessels rammed a Philippine Navy supply boat, boarded Philippine craft, damaged communications equipment, seized firearms, and left several personnel injured, including one sailor who lost a thumb. Manila publicized the incident within hours under its policy of “assertive transparency,” releasing video footage and detailed accounts. By early 2025, Chinese officials were openly tying such coercive law-enforcement actions to the defense of a clearly articulated “red line” against new occupation.
The case above illustrates that maritime order in Asia is now shaped less by isolated crises than by the gradual hardening of operational limits. Across the South China Sea and adjacent waters, states are refining the boundaries of acceptable conduct through repeated encounters, legal positioning, and force posture adjustments. I conceptualize these limits as “red lines.” These red lines are increasingly observable though largely implicit, yet competition remains deliberately contained below the threshold of open naval conflict.
One of the most consequential shifts has been the normalization of sustained constabulary presence inside contested exclusive economic zones (EEZs). “White hull” forces – coast guards and maritime militias – now form an anchor to frontline competition. Their expanding patrol patterns allow states to assert claims, shadow rivals, and obstruct activities without escalating to overt naval warfare. Regional responses mirror this evolution: rather than deploy grey hulls, governments have invested heavily in coast guard fleets, maritime surveillance, and law-enforcement capacity. Competition has intensified, but has done so in a calibrated way.
Beijing’s main distinction is not between activity and inactivity but between reinforcement and expansion. Vietnam’s recent campaign of territorial reclamation underscores this difference. Satellite imagery shows that from mid-2024, Vietnam created roughly 600-640 acres of new land in the Spratlys within ten months, following a record pace of reclamation in late 2023. At Barque Canada Reef, dredging since 2023 has produced a 4.3-kilometre sandbar and the beginnings of an airstrip, with total reclaimed area reaching approximately 2.8 square kilometers by mid-2025. South Reef has expanded to roughly 0.68 square kilometers, now featuring multi-story bunkers and a harbor.
Yet these expansions have occurred almost entirely at long-held Vietnamese outposts. Beijing has protested but avoided large-scale operational escalation. The pattern reinforces the impression that China’s enforcement rubric tolerates substantial consolidation so long as it does not cross into occupation of previously unoccupied features.
Elsewhere, a similar hardening is evident
Around the Senkaku/Diaoyu Islands, Chinese coast guard vessels have maintained an unbroken presence in the islands’ contiguous zone throughout 2025, with continuous patrol streaks exceeding 250 days. Japan’s response has been steady, albeit restrained. The Japan Coast Guard has expanded round-the-clock aerial surveillance from Ishigaki and Naha, requested a significantly enlarged 2026 budget – approximately ¥317.7 billion ($2.1 billion USD) – for larger patrol vessels and additional unmanned aerial vehicles, and strengthened patrol rotations. Japan’s 2025 National Defense Strategy places greater emphasis on deterrence in the Southwest Islands, yet continues to frame these steps as defensive and aimed at avoiding direct confrontation.
Indonesia’s experience in the North Natuna Sea demonstrates a different form of red line enforcement. In October 2024, Indonesia’s maritime security agency (Bakamla) twice detected and expelled China Coast Guard vessel 5402 after it disrupted a Pertamina-contracted seismic survey by the MV Geo Coral on Indonesia’s continental shelf. Jakarta publicly described the incident as interference in lawful survey activity under the U.N. Convention on the Law of the Sea (UNCLOS). It also reiterated that China’s “nine-dash line” lacks any legal basis, emphasizing that the episode was a law-enforcement matter rather than a military crisis. In this way, Jakarta managed to defend its sovereign rights while avoiding escalation.
Malaysia’s pattern of responses has been subtler. China Coast Guard vessels now patrol with regularity near hydrocarbon projects off Sarawak and at Luconia Shoals. Malaysian naval or maritime enforcement vessels occasionally shadow these patrols, but generally have chosen not to escalate. The Chinese presence often challenges survey or support ships but typically stops short of physically halting drilling operations. The practical red line for Kuala Lumpur appears to lie in direct interference with core production rather than simple proximity. Malaysia continues to explore for resources, while managing incidents quietly and avoiding them escalating into a diplomatic crisis.
The Philippines occupies the most openly contested space in the South China Sea. Since 2023, its coast guard has systematically released videos, AIS tracks, and timelines documenting the long line of water-cannoning, ramming, and blocking incidents at Second Thomas Shoal and Scarborough Shoal. During the June 2024 clash, detailed footage of China’s boarding and equipment seizures circulated globally within hours. Transparency serves the purpose of consolidating domestic support and mobilizing diplomatic backing.
Yet the available evidence suggests that it has not moderated China’s operational posture. As a result, alliance signaling has grown more prominent. Expansion of U.S. military access to Philippine bases and increasingly complex joint exercises with the U.S. reinforce Manila’s message that lethal force or large-scale construction at contested features could trigger treaty consultations.
These developments suggest that Asia’s maritime red lines are hardening and that these dynamics are reshaping Asia’s maritime order. China Coast Guard patrols around energy fields near Vanguard Bank and Luconia Shoals, their near-constant presence around the Senkakus, Vietnam’s unprecedented land reclamation effort, Indonesia’s UNCLOS-based expulsions in the North Natuna Sea, and the Philippines’ highly publicized clashes with Chinese coast guard vessels all coexist within a shared, if contested, understanding of what constitutes “measures short of war.”
Competition has intensified across maritime Asia. Yet most actors are still avoiding the abrupt occupation of new features or direct navy-on-navy clashes, suggesting that restraint remains the order of the day despite increasing hostility underpinned by contested red lines. Maritime Asia’s order is therefore neither stable nor collapsing. It is being renegotiated in real time, through repeated close-quarters encounters that define how far states can go – and how far they are not yet prepared to push.
