Police said armed officers along with officers from the National Crime Agency cordoned off part of Rosier Business Park in Billingshurst this afternoon (May 17).
The vehicle was believed to contain firearms and explosives and was examined by military ordnance staff.
A lorry driver was arrested safely and without untoward incident, officers added.
No homes were evacuated and police said there is not threat to the local community.
A spokesman for Sussex Police: “Armed officers from Sussex Police assisted National Crime Agency (NCA) officers in the arrest of a driver of a lorry at Rosier Business Park in Billingshurst today, Thursday (17 May).
“The arrest was carried out safely and without untoward incident.
“In view of the possible presence of firearms and explosives in the vehicle, the area around the vehicle was cordoned off as a precaution while military ordnance staff examined the lorry to ensure that it and its contents are safe.
“The Business Park itself was evacuated as precaution but there have been no evacuations of residential areas and local people remain safe. There is no threat to the local community.
“Local officers are present to manage the cordons around the site.”