The line links the presidential Blue House in Seoul with the Pyongyang office of the nuclear-armed North's State Affairs Commission, which Kim chairs - one of his most important titles.

"The historic connection of the hotline between the leaders of the two Koreas has just been established," said senior Blue House official Youn Kun-young, adding that a test conversation between officials lasted 4 minutes and 19 seconds.

It is the latest step in a whirlwind of diplomacy on and around the Korean peninsula, triggered by the Winter Olympics in the South.

Moon and Kim are due to meet on Friday on the southern side of the DMZ, in what will be only the third inter-Korean summit since the 1950-53 Korean War ended with an armistice rather than a peace treaty, leaving them technically still in a state of conflict.

Seoul is pushing for a declaration that the war is over as a prelude to the signed of a treaty, with Moon declaring Thursday it was a goal that "must be pursued".

US President Donald Trump, who is expected to hold his own much-anticipated summit with Kim later, previously offered his "blessing" for the two Koreas to discuss a treaty.