The incident, which is yet to be confirmed, was reported at around 7.42pm by a concerned member of the public in Castle Street, Hastings, East Sussex.
Police said an unknown liquid was reported to have been thrown over two young men – however their whereabouts and the extent of their injuries are unknown at this stage.
A police spokesman said: “Officers are keen to identify those involved to ensure their welfare and pursue any potential criminal activity.”
The victims, described as being of mixed race and in their late teens, made off from the scene in the direction of the Old Town prior to police arrival.
It is unknown when or where the alleged attack occurred, police said.
Anyone with any information is asked to report it online or call 101 quoting serial 1137 of 13/10.
In an emergency, dial 999.
Alternatively, you can visit the Crimestoppers website or contact the independent charity anonymously on 0800 555 111.
The incident is not being treated as terror-related, police added.