TAIPEI (Taiwan News) — Staff at a social care office in the South Korean city of Ulsan experienced breathing difficulties after opening a parcel sent from Taiwan, reports said Friday (July 21).

After the incident was reported by the media, similar cases emerged on the island of Jeju and in the city of Daejeon, per CNA. In the first instance, a care organization for the disabled received a yellow plastic parcel from Taiwan on (Thursday) July 20.

Three employees suffered from dizziness and had difficulty breathing after they opened the package. While they suspected a chemical attack, police said they could not find any harmful substance after an initial inspection.

While they passed on the parcel to a defense research institute, police said the incident might be an example of a “brushing scam.” A box of unordered goods is sent to an address discovered online by a company, which posts fake positive reviews of its products to improve its ratings.

In Jeju, a resident took a box he had received from Taiwan to the police after watching a news report about the incident in Ulsan. The parcel contained cosmetics, but the recipient did not report any health problems.

Police in Daejeon said Friday they had found two similar incidents, with packages sent from Taiwan and Uzbekistan and containing unsolicited items. While they did not cause any health problems, police warned residents to contact them if they received unordered packages from Taiwan, CNA reported.

Taiwan's Criminal Investigation Bureau (CIB) said the package in the Ulsan case might have first been sent from another country to Taiwan, before Chunghwa Post mailed it on to South Korea. The CIB also said it was cooperating with the South Korean authorities to find out who was behind the incident, per CNA.