It’s troublesome when Chinese trawlers show up in the most dangerous waters off the Korean Peninsula. It’s even more alarming when they’re gone.

"It’s a bad omen,” said Choi Ohk-sun, a 65-year-old resident on the South Korean island of Yeonpyeong. The last time that happened was a decade ago, when North Korean artillery rained down on the island, destroying homes a few minutes’ walk from where Choi was picking mulberries late last month.

The Chinese trawlers left the north side of the fertile fishing ground that straddles the two Koreas for a few days after Pyongyang blew up a liaison office built by Seoul and warned of further provocations. Some worried that their exit foreshadowed another military action as tensions ramped between South Korean President Moon Jae-in and North Korean leader Kim Jong Un.