Detectives in Borehamwood are appealing for information following a "disturbance" in the town.
Police say they were called late on Monday (March 28) to Rossington Avenue to reports of a disturbance in the street.
But when officers arrived at around 11.55pm, anyone involved in the alleged incident had fled the scene.
Hertfordshire Constabulary has added that it has received no reports since of anyone being injured or coming to any harm.
It's believed a helicopter was also involved in the police response.
No further detail has been issued about what may have happened but police say "extensive enquiries" are being carried out to establish the circumstances surrounding whatever prompted police to attend.
Investigator Kay Leverton, from the Borehamwood Local Crime Unit, said: "We are now turning to the public for their help, to ask if they witnessed or heard anything in the vicinity of the Rossington Avenue area in the late hours of Monday night.
"Any information, even something that may seem relatively minor or insignificant, could be key to helping us progress our investigation."
You can email Investigator Leverton at kay.leverton@herts.police.uk or call 01 quoting reference 41/24826/22.
Alternatively you can contact Crimestoppers anonymously on 0800 555 111 or visit www.crimestoppers-uk.org.
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