Several vervet monkeys have been on the loose in St Louis, Missouri, since at least Thursday. City animal control officials said they do not know where the monkeys came from. Residents have been warned not to approach the monkeys, as they may be "unpredictable or aggressive under stress." The exact number of monkeys is unclear, but officials believe there is more than one. Early reports said there were four. The St Louis health department, which handles animal control, has been searching for the monkeys but had not found them as of Sunday evening. A primate expert from the St Louis Zoo identified them as vervet monkeys. These monkeys are small, with pale fur and black faces, and are native to Africa. Justen Hauser, the bureau chief of environmental health for St Louis, said, "At this time, we do not know where these animals came from." He added that owning exotic animals like monkeys is prohibited in the city, so officials do not know of any local homes keeping them illegally. Sightings have been reported in the O'Fallon Park neighbourhood, north of the city center. Hauser believes the monkeys remain in that area. Residents expressed concern; Marva Young told local news, "I think of the danger, because that's a wild animal." Others called the situation "crazy," noting the close proximity of the animals. Photos shared on social media show the monkeys perched on porch walls and standing near cars. Animal control officers have been patrolling but have yet to capture them. Hauser said, "We are working to get an idea of where they may be hiding or seeking food." He urged residents not to try to catch or approach the monkeys but to report sightings to the health department. Once caught, the monkeys will be sent to a certified facility for exotic animals. Though primate ownership is banned in St Louis, Missouri ranks high in primate ownership overall. A report last year noted that "at least 35 to 50 primates" are traded annually in the state. Vervet monkeys are not native to the US. However, a wild colony lives in Florida, descendants of escapees from a research centre near Fort Lauderdale from the 1940s.