A 53-year-old man has been arrested in connection with a blaze in a fireworks warehouse in the UK.
Staffordshire Police said the two people remain "unaccounted for" following the fire which broke out at the industrial unit at about 5.15pm yesterday.
The force said it was in contact with the missing people's family members.
Officers said a joint fire investigation had been launched into what caused an initial explosion at the SP Plastics building in Tilcon Avenue, Stafford.
Police Superintendent Ian Coxhead said: "We have a great deal of sensitive and challenging work to complete in order to allow us to establish the cause of the explosion and the following fire."
He added that a "significant volume of fireworks" was being stored on site, and the unit had been all but destroyed in the ensuing blaze.
Rescue workers planned to begin their search for the missing people once the premises were deemed safe.
Dramatic footage showed thick plumes of smoke and bursts of fireworks exploding in all directions from the factory - a scene a witness described as "horrendous".
At the height of the blaze, which took three hours to bring under control, 50 firefighters, eight engines and four specialist appliances were at the scene, the fire service said.
West Midlands Ambulance Service sent four ambulances, the Hazardous Area Response Team, four emergency doctors, five paramedic officers and two rapid response vehicles to the site.
Two men were taken to the University Hospital of North Staffordshire, one in his 60s suffering from a back injury and another, in his 40s, with serious burns.
Two women, one in her 40s and the other in her 50s, were assessed for smoke inhalation but discharged at the scene, police said.
A safety cordon was thrown up around the site of the factory, which had closed for the day by the time the fire broke out.
The fire was largely scaled down by around 11pm, the fire service spokesman said.
Police are investigating the cause, after what they described as "a challenging and complex operation" to deal with the blaze.
Some disruption was expected as Tilcon Avenue remained closed during the investigation, with some local businesses sealed off.
During the blaze Mike Hillman said he was watching from Tixall Road, adding: "Massive fire, loads of smoke this way, hope everyone is OK".
He tweeted: "Hoping everyone is OK over there, looks like it has spread down the whole row of units on that side of the estate."
Christina Harrison told BBC News: "My friend said: 'Oh, something has fallen on my head'. It turned out to be ash falling on us.
"As we got closer the smoke got worse and worse. You could just hear explosions and fireworks going off."