"Since the 1990s... we have gradually been building up wire (fencing) and border patrol roads in boundary areas," foreign ministry spokesman Liu Jianchao told journalists when asked about the fence.
"It is not appropriate for people to connect this with the current situation on the Korean peninsula."
South Korean and Western media reports have said China erected the barbed-wire fence shortly after North Korea conducted its first nuclear test on October 9.
The aim was to prevent an exodus of refugees from the isolated state, the reports said.
But Liu said China was not taking any extra border security measures along its more than 1,400-kilometer-long (870-mile) border with North Korea.
"The purpose is to improve the situation or condition for border control and to maintain good order in the control area, this is a normal construction activity," Liu said of the fence.
"As for as we know the China-North Korea boundary area is quite normal, everything is normal."
Locals in China's north-east city of Dandong, the major gateway to North Korea, said a section of the fence was being constructed for up to 40 kilometres along the Chinese side of the Yalu River that forms the border.
However they said construction of the fence in the Dandong region began as early as February.

Copyright AFP (Agence France-Presse), 2006