Hundreds of US marines have occupied Kandahar airport in the biggest deployment since the military set up base in the region.
Some Marines have landed at the airport in helicopters while others drove there in convoys.
As they passed through the city, Afghans have waved AK-47s and rocket-propelled grenade launchers in celebration.
But a military spokesman warned soldiers to be on their guard: "They are happy to see us, but be aware there are still a lot of people in there who don't like us," he said.
Marine vehicles have taken up posts on the perimeter of the airport. Meanwhile, soldiers have cleared debris from the terminal building and checked for mines and booby traps.
"We are currently sweeping the airport to determine where the minefields are," said a spokesman.
Kandahar International Airport was the scene of fierce fighting until the Taliban abandoned the city a week ago.