INCHEON, South Korea (AFP) - Three top North Korean officials, including the nuclear-armed nation's de facto number two, made a surprise visit to South Korea on Saturday and held the highest-level talks for years, fuelling hopes of a breakthrough in troubled cross-border ties.

The meeting had an immediate impact, with the two sides agreeing to resume a formal high-level dialogue that has been in limbo for seven months.

The extremely rare trip was ostensibly made to attend Saturday's closing ceremony of the Asian Games, but the trio went straight into a series of meetings with the South's top official for North Korean affairs, Unification Minister Ryoo Kihl-Jae, and President Park Geun-Hye's national security adviser Kim Kwan-Jin.

It was a marked turnaround after months of military tensions and vicious personal attacks in the North Korean state media against the "political prostitute" Park.

The delegation included the newly elected vice chairman of the National Defence Commission Hwang Pyong-So, who is widely seen as the second most powerful man in North Korea after paramount leader Kim Jong-Un.

With him was another Kim confidante, Choe Ryong-Hae, and Kim Yang-Gon who heads the ruling party's United Front Department in charge of South Korea-related affairs.

"This is a very big deal," said John Delury, a North Korea expert at Yonsei University in Seoul.

"If you are Park Geun-Hye and you want a credible channel to the leadership in Pyongyang, then this is your dream team," Delury said.

Kim Jong-Un has not been seen in public for a month, fuelling speculation about his health and even triggering rumours of a coup.

The South's Unification Ministry, which was only informed of the visit late Friday, said Park would have liked to meet the delegation, but it had not been possible to schedule a visit to the presidential Blue House.

During the talks, which lasted several hours, Choe thanked the South for the hospitality it had shown the North Korean athletes attending the Asiad in Incheon.

"I am proud that in the effort for reunification, the sports field is leading the way," said Choe, who heads the national Sports Commission.

North Korea has exceeded all expectations at the Games and, with just a handful of events remaining, lies seventh in the medals table with 11 golds.

But the North Korean officials made it clear that the Games were not the main focus.

"We have come here in the hope that this opportunity will provide a chance for the North and the South to strengthen their relations," Kim Yang-Gon said.

The two Koreas have remained technically at war since the end of the 1950-53 Korean conflict, and recent months have seen one of the regular spikes in cross-border tensions.

Infuriated by South Korea-US joint military exercises, the North carried out an extended series of rocket and missile launches into the Sea of Japan (East Sea).

TV footage of Saturday's talks showed Hwang, who holds the rank of vice marshal in the Korean People's Army, dressed in military uniform, while Choe and Kim both wore dark suits.

South Korean National Security Adviser Kim Kwan-Jim, who just months ago Pyongyang was describing as a "confrontation maniac", said the visit offered an important opportunity.

"As we have here people with very special positions in the North, we should make efforts to push relations forward," Kim said.

The two sides agreed to try and resume a high-level dialogue by late October or early November. The last round in February resulted in the North hosting a rare reunion of families separated by the Korean War.

As relations with its most important ally China have cooled, North Korea has gone on something of a diplomatic offensive of late, even sending its foreign minister to the UN General Assembly for the first time since 1999.

North Korea wants a resumption of six-party talks on its nuclear programme, but the United States and South Korea insist it must first make a tangible commitment to abandoning nuclear weapons.

The Unification Ministry said the three officials would fly back to Pyongyang on Saturday evening after watching the Asiad closing ceremony.