Some airlines have cancelled flights to Taipei and rerouted others using nearby airspace that has been closed to civilian traffic during Chinese military exercises sparked by US House of Representatives Speaker Nancy Pelosi's visit to Taiwan.
China deployed scores of planes and fired live missiles near Taiwan on Thursday in its biggest-ever drills in the Taiwan Strait, set to run until noon local time (0400 GMT) on Sunday in six zones encircling much of the island.
The airspace involved is comparatively small, but the disruption is hampering travel between Southeast Asia and Northeast Asia.
Korean Air Lines Co Ltd said it had cancelled flights between Seoul and Taipei on Friday and Saturday, and would delay a flight on Sunday due to the exercises.
Singapore Airlines Ltd said it had cancelled its Friday flights between Singapore and Taipei due to "evolving airspace restrictions" and would continue to monitor the situation in case more adjustments were needed.
Japan's ANA Holdings Inc and Japan Airlines Co Ltd are still operating flights to Taipei as normal, spokespeople for the airlines said, but are avoiding the affected airspace on those flights, as well as on routes to Hong Kong and Southeast Asia.
Hong Kong's Cathay Pacific Airways Ltd said on Thursday its flights were avoiding designated airspace zones around Taiwan, in a move that could lead to more flying time for some flights.
Flight tracking service FlightRadar24 showed Taiwanese carriers China Airlines Ltd and EVA Airways.TW were still flying to and from the island as of Friday morning, as was Philippine Airlines and cargo carriers FedEx Corp and United Parcel Service Inc, though avoiding the areas affected by the military drills.
Emirates was still scheduled to fly to Taipei on Friday, according to its website.
Taiwan, along with mainland China and Hong Kong, is one of the few places in the world that still requires quarantine for arrivals because of COVID-19, triggering reduced demand for travel to the island that means there are far fewer flights than before the pandemic.
OPSGROUP, an aviation industry cooperative that shares information on flight risks, said the Chinese military exercises would affect major routes between Southeast Asia and Northeast Asia, leading to re-routings that could take longer and burn extra fuel.
The airspace involved, however, is minor in its impact on the global aviation industry compared to the decision by most airlines to bypass overflight of other places like Russia, Ukraine, Afghanistan, North Korea, Iraq and Syria.
The avoidance of Russian airspace, for example, has led to a near four-hour increase in flight times between Finland and Japan.
Taiwan said on Wednesday it was negotiating with neighbouring Japan and the Philippines to find alternative aviation routes, the official Central News Agency (CNA) reported.