Nato has ordered a security lockdown at its massive base in central Afghanistan after a car surged on to an airfield and burst into flames just as the US defence secretary landed for an official visit.

The incident happened as Leon Panetta touched down at Camp Bastion in Helmand province and prompted a security alert as investigators tried to establish whether he was the target of an attack.

A man was pulled from the burning car and is being treated at a hospital on the base. Sources said the vehicle was about 100m from Panetta's aircraft when it crashed, and that neither he nor any members of his entourage were in any danger.

However, the Nato-led International Security and Assistance Force (Isaf) must now determine whether the driver, thought to be an Afghan, was involved in a failed terrorist plot. Though details are sketchy, the Pentagon confirmed the vehicle involved was a pickup truck that had been stolen from a soldier in a car-jacking shortly before it drove at speed on to the runway.

The truck headed for the ramp where Panetta's plane intended to stop but crashed into a ditch, where it burst into flames. Early reports suggested that no explosive material was found in the truck, but the driver was seriously injured.

A Pentagon spokesman, Navy Captain John Kirby, was quoted in the Washington Post saying: "I'm told he caught fire, the fire was put out, and he is being treated for his wounds. We are investigating this. We don't know what the motivations of the driver were."

Another Pentagon spokesman, George Little, told the Post: "Security personnel responded, and for reasons totally unknown to us at this time, our personnel discovered that he was ablaze. We don't know all the facts, but we have no indication that the secretary was ever at risk."

Isaf released a brief statement as Panetta, who was under the protection of US marines, continued his visit. It said: "[We are] aware of a stolen vehicle incident today at Camp Bastion which resulted in the injury of one coalition service member. The alleged perpetrator was apprehended by base security personnel and we are currently investigating to determine more facts. This incident took place this afternoon around the time US secretary of defence Leon Panetta was arriving in Afghanistan, at no point was the secretary or anyone on the aircraft in any danger."

David Cameron was asked about the incident during a joint press conference with President Obama on the White House lawn. "It is still very early and details are still coming through," the prime minister said. "We will want to examine and investigate what has happened. Security of our people and of the troops from both nations is a highest priority. If there are things that need to be done to keep them safe, then we will do them."

Although Isaf would not say for certain that this was a terrorist attack, tensions between the military and Afghan civilians are running high because of recent atrocities involving US forces.

Wednesday's incident comes amid widespread protests and unrest provoked by the killing of 16 civilians by an American soldier over the weekend. Just weeks ago, the White House was forced to apologise after American soldiers were caught burning copies of the Qur'an.

If it proves to be a terrorist incident, it will raise huge concerns about the security at Camp Bastion, a vast military base at the heart of the Nato-led effort against the Taliban. It has a 40km perimeter fence and, within it, is a separate US facility called Camp Leatherneck, which is the headquarters of the US marines. An Afghan army training centre is also within Bastion's boundaries, as well as the hospitals that treat all military casualties. Most British troops who serve in Helmand arrive at Camp Bastion on flights that come in under the cover of darkness to reduce the rise of attack. It is the main supply hub for Nato's effort – food and ammunition are stockpiled on the base.

Because of this, security into and out of Bastion is tight, though the airfield is so large it is probably the most vulnerable to attack from a determined outsider. There are 20,000 to 30,000 people on the base and hundreds of local workers are allowed in to help with the building, cleaning and other support tasks that are needed to keep it running smoothly.

All of them are vetted to ensure the Taliban has not planted someone inside the base. This normally requires a worker needing a reference from a tribal elder.

After the incident, Panetta addressed American troops, telling them: "We'll be challenged by our enemy. We'll be challenged by ourselves. We'll be challenged by the hell of war itself. But none of that, none of that, must ever deter us from the mission that we must achieve."