POLICE officers in gas masks and radiation gear direct people into a decontamination tent, while paramedics tend to the walking wounded.
Elsewhere, people trapped inside nearby buildings are guided into a waiting tent where they will have their clothes bagged as the scale of the major radiation incident unfolds.
It sounds like something from a disaster movie, but that was the scenario which played out behind the walls of Portsmouth Naval Base yesterday.
The three emergency services descended upon the base as part of an exercise to put their response skills to the test.
It followed the scenario of an explosion which had unleashed radioactive materials on an inner city street.
Fortunately, none of it was real, and those involved were volunteers.
Jon Malley works for the Hampshire and Isle of Wight Local Resilience Forum, which assessed the exercise.
He said: ‘It all went very well and everybody put in a lot of hard work.
‘We are very grateful to the Ministry of Defence for letting us use the base.
‘Normally exercises like this would have to be done in a big car park or a field, which makes it difficult to get a real understanding of what it would be like.
‘Parts of the naval base are like any old city street so it was the perfect location.’
The event, named Exercise Cameron, mirrored the setting of a narrow city road with terraced housing.
Around 400 people took part including the emergency services, volunteers, Portsmouth City Council staff and students from South Downs College.
It lasted for around seven hours.
Members of the public were told beforehand not to panic if they saw large numbers of emergency services vehicles entering the base.