At roughly 7:30 p.m., residents reported seeing a "large white cloud" coming from a private residence on the island, according to Island County Sheriff Mark Brown.
A man who lives in the area of South Bartl Drive and Elger Bay Road also called 911 after he began experiencing breathing issues.
Medics arrived at the home and found a steel gas cylinder that appeared to be leaking chlorine, according to Camano Island Fire officials. The resident at the home was taken to a local hospital for treatment, and roughly 25 to 30 homes in the area were evacuated or told to shelter in place.
Three residents of nearby homes also were also taken to the hospital after they began experiencing breathing problems. Four firefighters also were sent to the hospital as a precaution. All were treated and released.
A Skagit County HAZMAT team was dispatched to the island to deal with the leak, and officials said the area should be clear by early Wednesday morning.
Chief Mike Ganz of Camano Island Fire & Rescue later said the leak was caused when the resident of the home, who owns a scrap metal business, cut into the cylinder and the gas vaporized. He said he had cut into other cylinders without a problem.