Police detained more than 20 people, mostly on curfew violations, on the first night of restrictions in downtown Los Angeles and used crowd-control projectiles to break up hundreds of protesters demonstrating against President Donald Trump’s immigration crackdown,

The mayor said the curfew will run from 8 p.m. to 6 a.m. local time, and cover roughly a square mile of downtown. She said she expects it to last several days.