Chinese fishing ships are reportedly leaving a disputed sea border that divides the two Koreas, following a nuclear test by the North on Monday.
Yonhap news agency on Friday quoted a South Korean army source as saying: "Chinese fishing vessels have begun retreating from NLL (northern limit line) waters since yesterday. We are working to find out if this is based on North Korea's request."
The NLL marks the maritime border between the two Koreas.
More than 280 Chinese vessels were fishing near there for crab earlier this week but the number has fallen to about 140, according to the source.
The North declared on Wednesday that it is no longer bound by the 1953 armistice that ended the Korean war.
The area around the NLL was the scene of bloody naval clashes in 1999 and 2002.
Meanwhile, a draft resolution being circulated among UN Security Council members after North Korea's latest nuclear test, urges UN members to immediately enforce previously approved sanctions against Pyongyang.
The draft says the council "condemns in the strongest terms the nuclear test conducted by (North Korea) on 25 May 2009 in flagrant violation and disregard of its relevant resolutions" and "calls upon all member states immediately to enforce the measures that were put in place by resolution 1718."
A UN diplomat said the preliminary draft was prepared by Japan and the United States. It will be discussed by the permanent council members, Japan and South Korea later on Thursday.
Sanctions were approved by the council after a nuclear test in 2006, but have not been enforced.
South Korea and the United States have raised their military alert levels after North Korea warned on Wednesday that it is no longer bound by the armistice that ended the 1950-53 Korean war and it was ready to attack.
The North KCNA news agency reported a commentary in a state newspaper as saying: "It's a matter of time when a fuse for war is triggered."