Three fire engines have been spotted in Carmelite Road in Harrow Weald following reports of chemical fumes.
Members of Harrow Online Group sent reports stating that emergency services were on the road but no fire could be seen.
The fumes are believed to have been caused by mixed cleaning products.
London Fire Brigade told Harrow Online: “Firefighters are currently investigating reports of chemical fumes due to mixed cleaning products.
“The Brigade was called at 1619. Two fire engines from Harrow and Northolt fire stations and a fire rescue unit from Wembley Fire Station are at the scene.”