A fake cigarette prompted armed police to swoop on a coach on the M6 Toll road and close the motorway for more than four hours.
Forty eight passengers on the Megabus Preston to London service were led off the coach and forced to sit apart in a cordon on the opposite carriageway.
The road was closed near Lichfield before police said they were no longer treating the incident as suspicious.
Police said they received a “genuine report” of vapour escaping from a bag.
Armed officers, troops, firefighters and bomb disposal experts all went to the scene.
Jenny Lister, who was on the coach, said when she got off “there were armed police aiming at us”.
She said: “We… were told to sit in rows and not talk to each other.”
A force spokeswoman said, given the credibility of the information received, officers “responded swiftly and proportionately”. But police found no crime had been committed.
The M6 Toll road was shut from about 08:20 BST and fully reopened by 14:00 BST northbound and by 15:00 BST southbound.
Staffordshire Police received a report from someone who saw vapour coming from the man’s bag while the coach was near the M6 Toll plaza at Weeford, near Lichfield.
The force said on investigation they found the passenger had an electronic cigarette which produces a visible vapour.
The passengers, including at least one young boy, were taken to a cordoned-off area of the motorway and surrounded by police.
A decontamination unit was set up and officers searched the coach passengers one by one.
Military personnel, police dog handlers, firefighters and other specialist units were at the scene.
No-one was injured, there was no danger to passengers and no-one was being treated as a suspect after armed officers evacuated the Megabus coach, police said.
The spokeswoman said: “We can now confirm that, whilst this was a genuine security alert, the significant concerns reported to us were unfounded.
“It’s important to state that no criminal offence has been committed and no passenger or any other member of the public is being treated as a suspect.
“We would like to apologise for any inconvenience and hope that the public understand that we have our duty to safeguard public safety.” …