Emergency services were called to an address in Pattison Street, Leith, in Edinburgh following reports of a substance spilling in the fourth floor of a flat at around 3.30pm yesterday.
A Police Scotland spokesman for the Lothians and Scottish Borders Division refused to describe it as a chemical incident but could comment no further about what was discovered.
He said a member of the public had initially called the ambulance service concerned they may have come into contact with a hazardous substance.
While residents living near to the block were evacuated, a spokesman said there were "no health concerns for any other individuals who were in the address".
Four firefighters wearing what appeared to be hazard protection suits were seen entering the building.
A woman was taken to the Edinburgh Royal Infirmary and it is believed that her young child, who was with her at the time, was being looked after by relatives.