BEIJING — The last time Abdulhamid Tursun spoke to his wife, she was huddled in a Beijing hotel room with their four children, frightened after being evicted from the Belgian Embassy in the dead of night. Suddenly, plainclothes police officers burst into the room, cutting off the couple’s video call.

Mr. Tursun says he has not heard from her since.

His wife, Wureyetiguli Abula, 43, had gone to the Belgian Embassy to seek visas so the family — from the Uighur Muslim minority group — could be reunited with Mr. Tursun, 51, in Brussels, where he won asylum in 2017.

But instead of finding protection, Ms. Abula and her children, ages 5 to 17, were dragged away after the Chinese police were allowed to enter the embassy.

Now the case is raising alarms back in Belgium, where lawmakers are asking how it could have happened and where Mr. Tursun’s family has been taken. It illustrates how, two years after China began detaining Uighurs in a vast network of internment camps, the group has limited protections — even from Western democracies — against persecution by the Chinese government.