Officers were called to a building site on Whyteleafe Hill around 3.10pm today (August 12) after the discovery was made.
The road was closed in both directions and a cordon remains in place.
One local reported hearing “a big bang” around 7.45pm.
Whyteleafe straddles the border of Surrey and Croydon, with some parts being included in the London borough.
A Surrey Police spokesperson said: “A road closure is currently in place in Whyteleafe following the discovery of a suspicious device at a building site earlier today.
“Officers were called around 3.10pm and are currently still in attendance at the location, along with colleagues from Surrey Fire and Rescue Service.
“A cordon is in place and a bomb disposal unit is en route.
“Whyteleafe Hill has been closed in both directions and we urge motorists to seek an alternative route.
“We will provide further updates as and when we are able to.”
