The Democratic People's Republic of Korea (DPRK) Wednesday fired three rounds of artillery near disputed Yellow Sea border with South Korea, Yonhap news agency reported, in the second such incident in one day.

The agency?got the information from local residents, and there was no immediate official confirmation. Earlier on Wednesday, ROK Marines?returned?warning shots after a DPRK shell landed near the sea border.

An ROK Defense Ministry official said the first rounds of shells fired by the DPRK landed in the waters off Yeonpyeong Island, but it was?not?certain?whether it was inside the ROK's territorial waters. Yonhap said ROK fired back with its artillery.

"Three shots were heard. One shell landed near the Northern Limit Line (NLL)," Yonhap quoted a military official as saying.?

An anonymous government official said: "One shot (from the DRPK) crossed the NLL, but I don't think it's something serious".

Yonhap said the shelling started around 2 pm local time.

?"We could not get visual confirmation about where the DPRK's shells landed, and we needed to use equipment to assess where they landed,"?a defence official explained why ROK responded an hour later.

ROK officials did not specify where ROK launched the artillery fire, but it appeared to be from a marine unit based on the island.

After the initial exchange of fire, an ROK Defense Ministry spokesman said, "The situation is now stable. After we fired back, there was no further response from the DRPK. We are still on alert."

Fishing boats in the vicinity were called to port, and Yeonpyeong residents were evacuated to emergency shelters, media reports said.

Wednesday's incident came after the DPRK made apparent peace overtures and expressed interest in?resumption of?the stalled Six-Party Talks.

Envoys from the DPRK and ROK held rare talks in Bali last month, and a senior DPRK official visited New York later for discussions with US officials.

The first artillery fire seemed more like an intentional strategy of the DPRK than a simple accident,?Zhang Liangui, a Beijing-based expert on Korean studies, told China Daily.

As the DPRK is facing growing domestic difficulties in dealing with its food shortage and recent flooding, it wants to put more pressure on Lee Myung-bak's government as a way to leverage more aid, according to Zhang.

"The incident is also intended to 'produce tension' so as to put more pressure on the United States," he told China Daily.

China was closely watching for further developments in the incident, but it is not likely to escalate further because there were no casualties and the situation did not deteriorate, said Ma Dingsheng, a commentator for Hong Kong-based Phoenix TV, in an interview.

"After all, they know each other's bottom line too well,"?Zhang said.

In November, the DPRK shelled Yeonpyeong,?and four?people including 2 civilians were killed.?The DPRK said it was responding to an ROK artillery drill, which encroached upon its waters.