Firecrackers and white balloons filled the skies near the border as a five-car train started rolling north on a restored track on the west side of the peninsula. On the eastern side, a North Korean train crossed into the South on another reconnected rail line where it was greeted by children bearing flowers.
It was the first train crossing of the 2.5-mile-wide no man's land dividing the two sides since inter-Korean rail links were cut off early in the 1950-53 Korean War.
The trial run was the latest symbol of a historic reconciliation that the longtime foes began pursuing with the first-ever summit of their leaders in 2000. That summit has led to a series of exchange projects, including the opening of cross-border roads that thousands of South Koreans cross each year as tourists, or to work in special enclaves in the North.
The detente has often stalled, mainly because of tensions over North Korea's nuclear programs.
Thursday's one-time test run came after repeated delays since the rail lines were linked in 2003.
"It is not simply a test run. It means reconnecting the severed bloodline of our people. It means that the heart of the Korean peninsula is beating again," Unification Minister Lee Jae-joung said at a ceremony at Munsan station, about 8 miles south of the Demilitarized Zone, before boarding the train.
The two Koreas "should not be derailed from the track or hesitate" in their moves toward unification, North Korean Senior Cabinet Councilor Kwon Ho Ung said.
However, Kwon also repeated the North's claims that outside powers — usually a reference to the United States — were the main obstacle to reconciliation between the Koreas.
"Even at this point, challenges are continuing from divisive forces at home and abroad who don't like reconciliation and unification of our people," Kwon said.
South Korean President Roh Moo-hyun watched the event live on television, hailing it as a "result of building trust consistently with patience," his office said.
Not long after, the North Korean train arrived in the South with one railcar bearing a sign that read, "The car that great leader and comrade Kim Il Sung boarded in person on Aug. 9, 1968" — referring to the North's late founder and father of current leader Kim Jong Il.
The trains, each carrying 150 people from both sides, returned to their origin later Thursday.
While the rail crossing symbolized reconciliation for some, it was a reminder of loss for others. A dozen South Koreans whose relatives allegedly have been abducted by North Korea staged a protest outside the Munsan station, demanding Seoul do more to bring their loved ones home.
"I wish the train would come back with my son if he is still alive," said Lee Kan-shim, 72, bursting into tears as police kept her from the site.
One of the passengers on the South Korean train, Yang Hyun-wook, head of the Seoul office of the Korea Railway Corporation, said the journey would be emotional.
"I think it should have happened earlier, but I hope this will be an opportunity for South and North Korea to become one," Yang, 55, said before boarding.
Yang Seok-hwan, 75, who was born just south of the border in an area where no civilians are now allowed, thought he would be able to take the train when some community officials asked him to attend the ceremony.
"I'm disappointed. I thought I could take the train if I came here," he said. "My hometown is just over there, but I haven't seen it for 50 years. I want to see my hometown again before I die."
It remains unclear when regular train service between the two Koreas could start. North Korea's communist government is extremely reluctant to allow many foreign influences into the country as it seeks to maintain its grasp on power.
The Korean War ended in a cease-fire that has never been replaced with a peace treaty — leaving the two Koreas technically at war.
The two Koreas resumed their rapprochement after North Korea agreed in February to take initial steps to dismantle its nuclear weapons programs.
Pyongyang failed to shut down its sole bomb-making reactor by a mid-April deadline under that agreement with the U.S. and other regional powers. The North has said it will not move to disarm until a separate dispute over frozen funds is resolved, but that has been held up by technical issues involved in transferring $25 million in its accounts.
Outside the Munsan station, about 40 people set pictures of North Korean leader Kim Jong Il aflame.
"They are all Reds," said a 78-year-old protester who would only gave his family name, Kim, while holding a sign that read, "Down With Kim Jong Il."
"We're lavishing aid to the North so that they can invade us more easily," he said.