Chinese students from the Uighur ethnic minority have been detained in Egypt in a broad police sweep that has shaken the country’s sizeable Uighur student and expatriate community, activists have said.

Egyptian police have detained scores of Uighur students, including 20 from Cairo’s Al-Azhar University who were stopped in the city of Alexandria on their way out of the country late Wednesday and told they would be deported to China, said Abduweli Ayup, a Uighur activist in Turkey.

Mr. Ayup said he had heard directly from some of the detainees and their relatives.

The detentions come amid reports that authorities in the Uighur homeland of Xinjiang in western China are seeking the immediate return of Uighurs studying abroad.

Authorities in Xinjiang have significantly tightened security measures in the past year, as well as controls on religious expression, in what officials characterize as an “unyielding” campaign against Islamic extremism brewing in the region.

Overseas Uighurs and human rights groups say the measures have turned Xinjiang into a police state with widespread arbitrary detentions and invasive surveillance.

The detentions in Egypt, a popular destination for religious study among China’s Muslims, were seen by activists as a possible sign that China’s security crackdown in Xinjiang is extending its reach overseas.

A Chinese foreign ministry spokesman appeared to acknowledge on Thursday that Chinese citizens had been detained in Egypt, saying at a regular briefing that consular officials would visit them. He gave no further details.

Another activist, who spoke on condition of anonymity for fear of reprisals, said overseas groups had managed to move 60 Uighur students out of Egypt to safety in Turkey this week, but 20 were held while trying to fly to Dubai.

Lucia Parrucci, a spokeswoman for the Unrepresented Nations and Peoples Organization advocacy group, said that a July 1 raid at the Asian restaurant in Nasr City caught 37 Uighurs, mostly student patrons and restaurant workers.

Unverified videos shared on social media purportedly showed more than 70 Uighurs sitting on a floor in a government building and others being driven in a truck in handcuffs.

Abdullah, an Asian student of Islam at Al-Azhar university, said Uighurs were being detained in the Hay el Sabia area of Cairo’s Nasr City district. He gave only his first name for fear of reprisals.