A 76-year-old woman suffered serious injuries while travelling on a bus in Burnley.
Police said the woman had boarded a bus close to the Spar store on Padiham Road, just before noon on February 27, when the incident occurred.
Officers understand that the pensioner suffered a serious neck injury as she was attempting to sit down.
Sgt Claire Pearson said: “We are trying to establish why this lady has fallen and so we are keen to speak to anyone who was on the bus at the time.
“We know there were several people on the bus at the time and so I would ask anyone that was to contact us if they saw what happened.”
Possible witnesses are being asked to call PC Bolton at Lancashire Police on the non-emergency number 101, quoting log number LC-20140303-1041.