One of two new tunnels at North Korea's nuclear test site was damaged by a recent typhoon and heavy rains, but appears to have only minor damage, a Seoul government source said Wednesday.

North Korea has built two new tunnels at Punggye-ri in the northeastern province of North Hamgyong, where the North conducted atomic tests in 2006 and 2009, in a possible preparation for its third underground nuclear test.

"It appears that one of two newly-dug tunnels at Punggye-ri was damaged by a typhoon and heavy rains," the source said on condition of anonymity.

However, the source said, the damage was not severe but only soil erosion at the tunnel entrance.

Concerns persist that North Korea might carry out a third underground nuclear test after its much-hyped launch of a long-range missile fizzled in April. Media outlets have reported the North appears to have completed preparations for such a test.

"It is not the situation that North Korea could not conduct a nuclear test because there is another new tunnel, if the North puts its mind to it," the source said.

North Korea's previous launches of long-range missiles in 2006 and 2009 were followed by nuclear tests. The international community has warned the North, already under U.N. sanctions for the nuclear tests, that it will face tougher sanctions if it goes ahead with another test.

North Korea was hit by two typhoons and severe floods in recent months, which left hundreds of people killed or missing. (Yonhap News)