The incident happened on a No 205 heading west from Whitechapel to Padd-ington. After establishing a cordon around the scene, Police said the incident had not proved suspicious.
Njazi Ismaili, 36, the owner of a laundry on Gray's Inn Road, rushed to help as passengers tried to clamber down. "People were jumping out of the top of the bus. They had forced the emergency window open and were so scared they were just trying to throw themselves out onto the road.
"I rushed over and began catching people and trying to help them down. At the same time I had my mobile phone in one of my hands as I tried to ring 999."
"I thought there must have been a bomb on the bus and you don't know whether to try and help people or to run and try and save your own life. I decided to help and there must have been more than 10 people who jumped out."
A female passenger is understood to have received treatment at the scene, but witnesses said many of the other passengers fled in fright and were seen running towards King's Cross.
Streets around Gray's Inn Road and the King's Cross end of Euston Road were quickly cordoned off and police, fire and ambulance services all attended.
Some passengers were said to have suffered from smoke inhalation. "Everyone panicked, but it was only a small fire and no one was hurt," police said. The fire was probably caused by engine trouble.
A London Fire Brigade spokesman added: "There was a small fire on a bus and it seems there was a bag found as well. Nobody was injured."Reuse content