A strong and unidentified “bitter” smell was reported by multiple residents throughout the city of Ashdod Thursday morning, spurring police forces, Environment Protection Ministry officials and fire fighting teams to conduct a widespread search for the origin of the mysterious odor.

Police ordered Ashdod residents to air out closed spaces and apartment buildings, but asserted that the public’s health was not at risk.

The stench was originally assumed to have come from a ship near the city’s port, though later reports ruled out such a possibility. Police asserted that the smell originated at a local factory and continued investigation to uncover the odor’s source, Channel 2 News reported.

Nine children reported feeling sick because of the smell.

In the afternoon, the smell was reported to have passed, though police warned that another wave may follow in the evening hours, as an additional chemical cloud was discovered on the city’s outskirts.