Two men have been taken to hospital with serious burns after being doused in a hazardous substance, believed to be acid.
Witnesses said they heard screams of "help me, help me" following the suspected acid attack, which took place in Stourbridge, West Midlands this morning.
Police and ambulance crews rushed to the scene at around 10.30am.
No arrests have yet been made but police are now urging anyone to come forward if they have any information.
A minor crash also occurred at the scene in the aftermath of the incident, resulting in police closing the road.
A spokeswoman for West Midlands Police said: "Police are investigating after a potentially hazardous substance was thrown at two men while sat in a van on Wollaston Road in the Stourbridge area of Dudley just before 10.30am this morning (Sun).
"The men have been taken to hospital with serious burn injuries as enquiries continue to establish the circumstances around the incident.
"The road has been closed following a minor collision which resulted after the attack.
"Anyone with information is asked to contact us via Live Chat at www.west-midlands.police.uk 8am - midnight, or call 101 anytime.
"To remain anonymous please call Crimestoppers on 0800 555 111. Quote log number 926 of September 1."
