The two sides normally speak twice a day during the week on the hotline, which has been in place since 1971.
However, Agence France-Presse quoted a spokeswoman for the South's Unification Ministry as saying:
"The North did not answer our call this morning."
Pyongyang also threatened both South Korea and the US with nuclear attack.
The threats come in the wake of new UN sanctions against Kim Jong Un’s communist regime, which followed the North's nuclear test in February.
North Korea has severed contact with the South as many as five times, most recently in 2010, after 50 South Koreans were killed in attacks ordered by Pyongyang.
Pyongyang has condemned joint US-South Korean maneuvers as an invasion rehearsal.
The current two-week computer simulated exercise, "Key Resolve," mobilized 10,000 Korean forces and 3,500 American personnel to test various conflict scenarios on the Korean peninsula, according to Yonhap news agency.
North Korea has said that the US mainland is within striking distance of its long-range missiles, though Washington maintains defenses capable of neutralizing a North Korean ballistic attack.
Bloomberg cited cited the North's state-run Rodong Sinmun newspaper as saying that North Korea was combat ready with strategic rockets and "diversified surgical nuclear strike mechanisms."