A mysterious illness struck a family and another individual in the stairwell of an apartment complex in Upplands Väsby, north of Stockholm, leading to sudden nausea and vomiting episodes.

The incident, which occurred on a Wednesday morning, also involved symptoms such as chest pressure.

The family, consisting of a father and two children, along with another man who arrived shortly after, experienced immediate relief upon leaving the building.

Emergency services, including the police and a special team from the fire department equipped with chemical diving gear and measurement tools, have responded to the scene.

The apartment complex has been cordoned off, trapping residents inside their homes.

Initial reports did not indicate any peculiar smell or sight at the location; however, some residents reported a stinging sensation.

The cause of the sickness remains unknown, and no criminal charges have been filed as the investigation continues.