LONDON (CNN) -- An alert on a bus that led armed police to close a major motorway near Birmingham, England, on Thursday is not terror-related, Staffordshire police said.
The M6 Toll motorway was shut in both directions after the alert was raised over "suspicious activity" by a passenger traveling on the bus from the northwestern town of Preston to London.
The incident came as Britain is in a state of heightened alert ahead of the Olympic Games, which open in London in three weeks.
Earlier Thursday, police in London arrested six people on terror charges, although they said the operation was not related to the Olympics.
In Staffordshire, armed police, firefighters and military bomb disposal units raced to the scene as the passengers were evacuated from the bus, which had pulled over near the town of Lichfield. Police in Britain are not usually armed when they respond to incidents.
But after conducting a search of passengers, their luggage and the vehicle, police said there were no injuries and no one is being treated as a suspect.
"Importantly, we are not treating this as a counterterrorism incident," Staffordshire police said in a statement.
"Given the nature of the report we responded swiftly and proportionately, treating the information as credible and extremely (serious). Our utmost priority was the safety and security of those people on the coach and those traveling on the motorway," it said.
"Following an initial assessment, we can confirm that no one has been injured and that there is no danger to passengers at the scene or any other travelers who were on the motorway at that time. We are also not treating anyone as a suspect."
Investigations at the scene continue, but passengers "have been put on another bus for their comfort and safety," the statement said.
A spokeswoman for Megabus said 48 people were booked on the bus involved in the alert.
"We are assisting police with their inquiries into an allegation made against a passenger," the spokeswoman said as the dramatic incident unfolded.
Footage from the scene showed the blue bus pulled over on to the hard shoulder, with the passengers sitting in rows on the tarmac where officers questioned them. Emergency vehicles could be seen lined up along the highway.
ITN reporter Rupert Evelyn told CNN from the scene that a woman with a small child was among the passengers led off the bus. A couple of military bomb disposal units were on standby, he said.
It is not yet known what caused the alert, but the police response appears to have been significant and swift.
Security has been stepped up in the United Kingdom as the London Olympics open later this month.
Five men and a woman were detained on terror charges Thursday morning, London's Metropolitan Police said.
The six, aged from 18 to 30, were all arrested on suspicion of the commission, preparation or instigation of acts of terrorism and are being questioned, police said.
Armed officers were involved in the operation. A taser was used on one suspect as he was arrested, but he did not need hospital treatment, police said.
Officers are searching homes in east, west and north London as well as business premises in east London.
The operation in London is not linked to the Olympic and Paralympic Games, the Metropolitan Police said.
Additional security measures will be in place in London and elsewhere during the Olympics.
They include the siting of missile defense systems around the capital and fighter jets on standby at air bases close to London.
CNN's Laura Perez Maestro, Claudia Rebaza