The massive construction projects were among agreements reached at a summit between South Korean President Roh Moo-hyun and North Korean leader Kim Jong Il in Pyongyang last month, only the second such meeting since the Korean peninsula was divided more than a half century ago.
Their prime ministers began talks on Wednesday to flesh out the agreements. It is the first time since 1992 that the two sides have held prime ministerial talks.
On Thursday, the two sides held three working-level sessions on the South's offers to repair a major North Korean road and a railway, build two shipyards there and provide medical assistance for the impoverished nation, Seoul's Unification Ministry said.
Details of the discussions were not immediately available.
Earlier on Wednesday, South Korean Prime Minister Han Duck-soo and his North Korean counterpart Kim Yong Il strolled through a Seoul hotel but did not yet meet for formal talks, leaving technical discussions to lower-level officials.
At the start of the talks on Wednesday, both Han and Kim called for quickly implementing the summit agreement, praising it as a big step toward reconciliation and peace on the divided peninsula.