HONG KONG — The pastor pulled on his respirator and ran directly into the fog of tear gas in central Hong Kong. He was trailed by a homemaker, a retired accountant and a middle-school teacher.

Undaunted by the pandemonium of gasping protesters, they pointed people to safety and poured saline into the eyes of those overcome by the fumes.

With their yellow vests and portable loudspeakers, Pastor Ka-Kit Ao and his volunteers are an unmistakable presence at the antigovernment protests that have upended this semiautonomous Chinese territory. They form human cordons between protesters and advancing police. They beg baton-swinging officers to go easy. And they solicit the names of those being hustled away in handcuffs so pro bono lawyers can follow up with assistance.

“I sometimes wonder whether we are doing anything of value, but we can’t just sit at home,” Pastor Ao, 34, said one recent afternoon before heading into the maelstrom with members of his group, Protect the Children.