SEOUL, South Korea -- North and South Korea exchanged gunfire at the border today while speculation mounted over the mystery of North Korean leader Kim Jong-un's absence from one of the country's most significant holidays.

North Korean military fired anti-aircraft machine guns at balloons that had been released into the sky by about 50 protesters at the border city of Paju, South Korea. The 10 balloons contained 200,000 leaflets, 1,000 U.S. dollars, 400 DVDs and 300 books showing life in South Korea.

When some of the shells fell south of the border, South Korean military gave a pre-warning, then fire a barrage of 40 bullets into the air towards North Korea.

North Korea has repeatedly warned that the propaganda balloon launches would be met with "regrettable merciless retaliation." Government officials said they did not know whether the North succeeded in shooting down the balloons.

Despite the cross-border gunfire, the attention of most North Korea watchers remained focused on Pyongyang to see whether Kim would appear at the 69th anniversary of the Worker's Party today. Kim remained a no-show and the state media only listed names of countries and people who sent congratulatory flowers marking the anniversary.

"The flowers had messages that said we pray for the respectable leader Kim Jong-un's good health," the male anchor read at the beginning of its main evening news.

Kim has not been seen in public since Sept. 3, sparking rumors that he may be seriously ill or could have lost grip of power in a quiet coup. But South Korea played down the rumors saying although the government could not confirm detailed status of Kim's health, his rule remains "in normal operation," Lim Byeong-cheol, spokesman for the south's unification ministry, told reporters today.

North Korean state television throughout the day aired documentaries on Kim with praises for his leadership and called for the people to stand behind their "eternal great general" who is "not afraid to sacrifice for the people."

Kim, thought to be 30 or 31, has been visibly limping during the summer and their state media did imply last month that he was not well, at one point describing Kim "in discomfort."

"The only thing proven so far is that he is not well. There's obviously something wrong with his feet or ankles. That, we know since we saw it. But there's no indication of political unrest," a senior South Korean government official told ABC News.

Some analysts in Seoul say the absence is intentional to draw attention from the international community.

"This could be a tactical silence. Kim Jong-Il {the father of the current leader} often would disappear from the public for more than 50 days in the past. They do this when they feel insecure about the stability of their regime from outside threat," said Ko Yoo-Hwan, professor of North Korean studies at Dongkuk University. "They do think that if there's a war, the leader's life is what the enemy is after. It's a message saying hey I can hide when needed."

Min-Jun Kim, Inyeong Kim, Minkyeung Cha contributed to this report