Police cordoned off a quiet residential road in Surbiton last night after bottles containing chemicals were found dumped on nearby wasteland.
A resident said five or six white plastic bottles, each one or two litres in size, were left near the green at the end of Elmbrige Avenue.
The fire service was called at 8.26pm, and sent three fire engines and two fire rescue units with specialist units.
They remained at the scene until 11.43pm.
The fire service declined to say what the chemicals were.
An Elmbridge Avenue resident said: "I have never seen so many emergency vehicles in my life.
"There were at least 30 emergency vehicles including police units and unmarked police cars.
"A police officer said it was a chemical problem.
"They cordoned off the roads and we thought should we get out or be evacuated.
"They were not very forthcoming about what was going on, but I suppose they did not want to scare us."
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