Mobile and criminal police in Hanoi launched night patrols in the city’s downtown districts on Tuesday night in an effort to cut crime. The patrols will be out from 11 p.m. to 5 a.m. every night until mid-January. Their prime targets will be crowded public places, as well as restaurants, karaoke parlors and dance clubs where guests may be asked to present their ID papers. Drivers out on the street late at night may also be stopped for random checks. Hanoi police also started checking the residency status of people living in the city earlier this month. The city of 7.6 million people is the second most crowded in Vietnam after Saigon, and population density in some downtown districts such as Ba Dinh and Hoan Kiem has exceeded 20,000 people per square kilometer. Local police have busted around 40 criminal organizations this year, including several violent debt collection gangs, according to a report by An Ninh Thu Do (Capital’s Security) news website. In February, the city also announced a target of busting up to 500 cases of illegal sex work this year, more than twice the number uncovered in previous years. Hanoi authorities last year identified more than 5,500 businesses offering so-called “sensitive” services. Most of them were registered as hair salons, bars or massage parlors, but also provided illegal sex services. Sex work is outlawed in Vietnam. Workers can be fined for providing services, while those procuring sex can receive jail time.