Over the years South Koreans have become accustomed to the warmongering threats and provocations of North Korea, often shrugging them off while the rest of the world reacts with horrified concern.

But with military tensions on the peninsula running at their highest level for years, there are signs of creeping public anxiety, especially following the North's nuclear test in February.

There has been none of the panic that saw people stripping store shelves in 1994 after a North Korean negotiator threatened to turn Seoul into "a sea of fire".

But South Korea's largest online marketplace, G-Market, saw a spike in sales of canned food and instant noodles after the North announced last week it was shredding the 1953 Korean War armistice and voiding peace pacts with Seoul.

According to the Asan Institute think-tank, which runs annual surveys on national public opinion, the number of South Koreans who believe a second Korean War is possible rose from 40 percent in 2010 to 59 percent in 2012.

"There may be a lack of outward reaction, but the perceived threat of North Korea is very real and growing," said institute analyst Karl Friedhoff.

And while only 7.8 percent of South Koreans cited South-North relations as the most important national issue in January this year, the figure doubled to 15.4 percent after the North's third nuclear test in February.

"I wasn't really worried until recently," said Park Soo-Mee, 38, a law office worker in Seoul.

"But people keep saying it feels different this time, and a close friend even said we may have to withdraw some cash in case the North attacks and the electricity is cut.

"My mother who lives in Canada keeps calling everyday to check on me."

The anxiety is most pronounced among inhabitants of the five "frontline islands" located near the disputed maritime border off the west coast of the Korean peninsula.

The South Korean military maintains a strong presence on all five, making them a prime target and one that has been chosen before by a North Korean regime seeking to flex its muscles.

In 2010 the North launched an artillery attack on Yeonpyeong island killing four people -- including two civilians -- and briefly triggering fears of a full-blown conflict.

In the past few days, North Korean leader Kim Jong-Un has inspected a number of artillery units which have their sights trained on the islands, telling them to prepare for "all-out war".

On his most recent tour Monday, he told artillery officers to be ready to turn targets on Baengnyeong island, which has a civilian population of around 5,000, into a "sea of flames".

Kim Young-Gu, a government official on Baengnyeong, said they had been holding daily drills to prepare in the event of a bombardment.

"It's not like there's a mass exodus of panicked islanders to the mainland. But to be honest with you, we're a bit scared," he told AFP by phone.

"We have left all the shelters open 24 hours and stocked them up with water and food in case something happens."

Yeonpyeong island still carries the scars of the 2010 shelling, which damaged a lot of housing that is yet to be fully repaired.

"These days, I go to bed with my clothes fully on so that I can bolt out of bed immediately if something happens," Cho Sun-Ok, a middle-aged woman living on Yeonpyeong, told SBS TV.

Another island resident whose house was hit in the 2010 shelling said he still felt traumatised by the incident.

"Since then, I can hardly get to sleep without getting drunk at night," he told Seoul's CBS radio.