Chinese air force jets briefly crossed over the midline of the Taiwan Strait on Monday and were tracked by Taiwanese missiles, Taiwan's government said, as US health chief Alex Azar visited the island to offer President Donald Trump's strong support.

Azar arrived in Taiwan on Sunday as the highest-level US official to visit in four decades, a trip condemned by China which claims the island as its own, further irritating Sino-US relations.

China, which promised...