One million people have volunteered to defend North Korea if hostilities break out with South Korea, the country's state media has reported.

The Korean Central News Agency claimed "young people across the Democratic People's Republic of Korea are turning out in the sacred war for defending the country with their faith and will to annihilate the enemies".

Tensions between the two countries are at their highest for some time after an exchange of fire on Thursday.

Top level officials from South Korea have been meeting North Korean officials at Panmunjom Truce village in a bid to calm the situation.

The office of South Korea's president said that the talks had resumed for a second day.

Delegates failed to reach agreement on Saturday in discussions that went on well into the night.

The North fired the first shot, according to Seoul, targeting huge loudspeakers which have been blaring propaganda across the border from South Korea.

North Korea later denied firing first.

The speakers were set up after two South Korean soldiers were injured by land mines while on patrol in the demilitarised zone which South Korea blamed on the North, something the North denied being responsible for.

Kim Jong-Un declared a "quasi-state of war" on Thursday after convening an emergency meeting of the communist country's military leaders, a South Korean news agency reported.

He ordered his military to be "fully ready" for war, according to Yonhap.

South Korea's military reported on Sunday that it has detected unusual troop and submarine movements in North Korea that indicated Pyongyang could be considering a possible strike.

About 70% of the North's 77 submarines have left their bases, the military said.

A South Korean official also said that the North had doubled the strength of its front-line artillery forces.

Several residents have been evacuated from some South Korean villages close to the border.

The first round of the talks started at around 6.30pm local time (10.30am Irish time) on Saturday, shortly after a deadline set by North Korea for the South to dismantle the loudspeakers.

UN Secretary-General Ban Ki-moon, a South Korean national, urged both sides to de-escalate the situation.