The M4 was closed in both directions on Saturday as firefighters battled a building fire blaze believed to involve fireworks.
Emergency services were called to the Westbrook area near RAF Welford in Newbury to an incident they said could be caused by pyrotechnics.
Explosions were heard by passersby, who filmed huge plumes of smoke rising above the site.
No injuries had been reported by Saturday evening.
The motorway was reopened at approximately 5.30pm.
Royal Berkshire Fire and Rescue Service said: “At 1.41pm on Saturday, 16 April, we received reports of a fire at an industrial building in Westbrook, Newbury.
“Two Royal Berkshire Fire and Rescue Service (RBFRS) crews from Newbury, one crew from Theale and two Officers have currently been sent to the scene, together with crews from Dorset and Wiltshire Fire and Rescue Service.
“Firefighters have found a fire involving possible pyrotechnics and fireworks. Cordons are in place, but people are urged to stay away from the area while emergency services deal with this fire.”
Debris landing on the M4 – two miles from the fire. Some fireworks!!!
In video woman interviewed in Boxford, said she decided to clear off due to a black cloud of smoke heading her way. Boxford south of the M4 maybe 3 miles from the explosion. There would definitely not be an industrial unit at that address, and would they allow fireworks even if there was. This is an MOD cover story for an explosion at the base, my opinion a Russian Mach 7 Khinsal missile the most likely cause, able to penetrate any bunker.