A church in the vicinity was then demolished in further proof of the country’s lack of religious freedom.
The 12 priests and seminarians were attending a retreat on 20 October in Gaocheng county, in Hebei province's Shijiazhuang city, when police struck, the Connecticut-based Cardinal Kung Foundation said in a statement reported by AFP.
The gathering was not supported by the government-sanctioned “Patriotic Association,” – the body that oversees all state-approved churches in China, the foundation said.
“They are charged with illegal assembly. I don't know if they will be released soon,” a worker at the detention center where the priests are being held told AFP.
Those arrested included Father Li Wenfeng, 31; Father Liu Heng, 29; Father Dou Shengxia, 37; seminarian Chen Rongfu, 21; seminarian Han Jianlu, 24 and seminarian Zhang Chongyou, 23.
Names of the others were unknown, the foundation said.
With regards the church, “we've demolished it,” the official said.
“It didn't have a license to conduct religious activities, nor construction and land use licenses,” he added.
“They are charged with illegal assembly. I don't know if they will be released soon”
A worker at the detention center where the priests are being held
An official from the Shahe city religious affairs office said another church was razed in June, two weeks after being built because it did not have proper building licenses.
Another official at the office refused to comment on how many local churches had been destroyed for similar reasons, but said such demolitions were justified.
“In China, one has to abide by Chinese laws,” he told AFP.
The latest arrests are one of a number of moves to stifle Catholicism in the region. In July, five other priests were arrested at Siliying village, also located in Hebei province, about 115 kilometres (70 miles) from Beijing.
Despite regulations, millions of Chinese worship at unofficial churches, some of which are more tolerated than others.