Police have launched a manhunt after a canister of what is believed to be tear gas was released during a fight on board a packed Tube train.
Several passengers were treated by paramedics for coughing and lack of breath after the noxious gas was released in the carriage.
The incident happened at Oxford Circus station at 9.13am this morning.
British Transport Police believe the gas was CS gas, which can also cause burning in the throat and nose.
Tube passenger Renae Brown was travelling on the northbound Victoria Line train from Green Park when the incident took place.
The 27-year-old, who was on her way to Oxford for her boyfriend's birthday, said: "We had just left Green Park when there was some commotion in the next carriage but we couldn't tell what was going on - we thought maybe someone had got their bag stuck in the door.
"Then these two men came through the door between the carriages and were stumbling, we thought they were drunk.
"That's when everyone started coughing and moving away, it wasn't nice.
"My initial thought was just to get away from it and I was hoping no-one would press the emergency alarm so we wouldn't get stuck.
"As soon as we got to Oxford Circus we just ran away, I didn't want to risk being near it, so we went and got on the Bakerloo Line.
"We've told the BTP about it and they might potentially need a statement, and TfL told us it wasn't toxic on Twitter."
Kate Howarth said: "Pretty scary experience on the Victoria Line this morning. Some sort of chemical let off and everyone on the tube started coughing uncontrollably."
Another passenger wrote on Twitter: "My throats still messed up. I did not need that just before a 12 hour shift. I'm coughing all over the place"
Officers believe the people in the images may have information that could help their investigation.
A TfL official wrote on Twitter: "We’ve been assured that the substance was not toxic, the BTP are aware of this customer incident & are investigating it fully."
Anyone who witnessed the incident, or who knows the identity of the men, is asked to contact BTP by texting 61016 or by calling 0800 40 50 40 quoting reference 171 of 20/07/19.
