The incident occurred 13 miles from the border with Syria, whose 33 months of conflict have fuelled sectarian violence in Lebanon, including a series of car bombings which have killed scores of Sunni and Shi'ite Muslims.
Security sources said Hezbollah officials, alerted to a suspicious car, began to follow it in two vehicles. The car then exploded.
It was unclear if the car detonated from the gunshots or if the driver set off the explosion. One report said a suicide bomber had caused multiple casualties, adding that ambulances rushed to the area, which was sealed off by the militant group and, later, the army.
Footage broadcast by Hezbollah's Al Manar television showed at least two damaged vehicles, one of them overturned, and piles of blackened, twisted metal scattered over a muddy and partially snow-covered plain.
The car which blew up was said to have been carrying about 110lb of explosives and its intended target was a nearby Hezbollah base. Villagers in the area also reported hearing gunfire.
Many Lebanese Sunni Muslims support the rebels fighting to overthrow Syrian President Bashar al-Assad, whose Alawite faith is an offshoot of Shi'ite Islam. Shi'ite Hezbollah has sent thousands of fighters to support Assad, while many Sunni jihadis have flocked to Syria to join the rebels.
The conflict has seeped back into Lebanon. Twin blasts struck the embassy of Iran - Hezbollah's patron - in Beirut last month. Bombs have also targeted Shi'ite districts of the capital and Sunni mosques in the northern city of Tripoli.
Hezbollah's participation in the civil war in Syria is highly divisive and unpopular in Lebanon, where many feel it has deviated from its original purpose of fighting Israel and that it has exposed the Shia community to retaliation.
The group's open support of Mr Assad left it with no shortage of enemies eager to strike at its leadership.