PAJU, South Korea - The two Koreas on Tuesday started their first regular train service since the 1950-1953 war by sending freight cars across their heavily armed border for a run hailed as a milestone in reconciliation.

The South has been pushing to re-open the rail link cut for more than half a century to shuttle goods to an industrial park it operates just inside the North where its manufacturing companies have access to cheap labour and land.

"With this service, a clogged blood vessel between North and South Korea has become unblocked," Yonhap news agency quoted an official at the South's Unification Ministry as saying.

A 12-car train carrying raw materials for shoes crossed into the North early in the morning and was due to return later on Tuesday.

The industrial park has been the main driver in pushing bilateral trade over $1 billion a year.

The daily freight service will run along on a route of some 20 km (12.5 miles) just inside the destitute North. The two agreed to the train service at an October summit.

South Korea had restored the railway tracks across the landmine strewn border but had struggled to win approval from the isolated North, nervous of any contact with the world.

North Korea earlier this year allowed a symbolic one-off crossing of trains. The two Koreas are technically still at war, having failed to sign a peace agreement to replace the ceasefire that ended their conflict.

South Korea's next wants to run its freight and passenger trains through the North to China and Russia and onto Europe.