Almost 50 people have been evacuated from a coach after armed police closed a major motorway.
The M6 toll road at Weeford near Lichfield was closed in both directions after allegations were made against one of the 48 passengers on board the Megabus coach from Preston to London, the coach firm said.
A spokeswoman for Megabus, which is operated by Stagecoach, said: "We are assisting police with their inquiries into an allegation made against a passenger who was travelling on board one of our services."
Reports suggested a man was seen pouring liquid into a smoking bag on board the coach. Armed police officers could be seen positioned next to the single-decker coach on the south-bound carriageway, as passengers were led off the vehicle one by one.
A number of emergency service vehicles were parked at the toll plaza, about 200 metres from the coach. Seven police vans arrived at the scene shortly before 11am.
It is understood the coach, which was heading south on the M6 toll road when it stopped, pulled over on to the hard shoulder of the motorway of its own volition.
The road has been closed in both directions between junctions three and four, the Highways Agency said. The incident is not thought to be linked to the arrests of six people in London as part of a pre-planned counter terrorism operation.
Several people, including at least one young boy, were seen sitting on the motorway in a cordoned-off square, several hundred metres from where the coach stopped.
Police surrounded the cordoned-off area, which spread across one lane of the toll road. Police dogs and their handlers were also seen walking nearby. Several other cordoned off areas could also be seen, along with what appeared to be bright yellow tents on the other side of the toll plaza.
Witness Nick Jones, who was stopped on the motorway for more than an hour and a half, told BBC News that police warned him to stay in his car, keep his windows closed and not to use air conditioning. He said: "I was beginning to feel a little uneasy. I was beginning to look around for an escape route."