This bustling South Korean capital has been defined for decades as a place of traffic jams and luxury shopping malls, long days of work and longer nights of drinking rice liquor. Residents rarely behaved as though their routines could be upended in minutes by the Kim regime to the north and its 10,000 artillery pieces.

But after years of largely ignoring threats from North Korea, some residents say they are becoming a bit jittery, with the ascension of an unpredictable young leader in Pyongyang and levels of hostile rhetoric not seen since the early 1990s.

Coffee shops here are still packed, and pop music pulses from storefronts, but South Koreans’ concerns are palpable in quieter moments. Their phones buzz with news updates on the North’s latest moves — its declaration of war; its announcement of plans to restart key nuclear facilities; its barricade of a joint industrial complex near the border. Children ask their parents what would happen if fighting broke out and where they would go for safety.

On Thursday, the fear spread to South Korea’s stock market, which suffered its biggest daily fall of the year. The South’s defense minister, Kim Kwan-jin, said the North had moved an intermediate-range missile to its eastern coast, perhaps for testing or drills.

“There could be war, or there could be peace,” said Joo Yang-yi, 26, a graduate student who studies North Korea.

Rather than play down the possibility of an attack, South Korean officials in recent days have emphasized their ability to strike back promptly. They have also welcomed recent U.S. shows of force in the region, including a brief deployment to the peninsula of nuclear-capable stealth bombers.

In the event of an attack, South Korea will “respond immediately without political consideration,” said a senior official who spoke on the condition of anonymity to share government thinking. “At the initial stage, South Korea is self-sufficient in terms of our ability to strike back. But [thereafter], we will need cooperation from the U.S. and neighbors.”

Divergence of opinions

South Koreans differ in their views of their increasingly belligerent northern neighbor. Some speak with confidence, saying the North’s near-daily threats are part of a coherent plan to force negotiations, not spark war. But others fear that the North’s new leader, Kim Jong Un, might push things too far, perhaps because he thinks he needs a major conflict to coalesce domestic support.

That divergence is reflected in public opinion polls. Over the past two months, the percentage of South Koreans who say the North is their top concern has more than tripled. Still, that represents just 26 percent of respondents; more South Koreans care about job creation than about Pyongyang.

Even the segment that is concerned about the North is far from panicking. During a crisis 20 years ago sparked by North Korea’s announced intent to withdraw from the nuclear Non-Proliferation Treaty, some in South Korea rushed to stock up on canned goods and water. This time, ­grocery-store shelves remain full.

“We have no alternative to remaining calm, because what we can do to personally prepare for emergency? Virtually nothing,” said Park Hyeong-jung, a North Korea researcher at Seoul’s Korea Institute for National Unification. “We live in a congested area of more than 10 million population. What a catastrophic chaos we will have if individuals begin to worry about tomorrow.”

Over the past several decades, Park said, South Koreans have been “gradually immunized” against the North’s threats. And for all the North’s recent bluster, nothing it has done lately compares with the galling attacks of the 1960s, ’70s and ’80s, which included hacking to death two U.S. troops in the demilitarized zone, numerous assassination attempts against South Korean presidents and the midair sabotage of a South Korean passenger plane.

After a fatal attack by the North in November 2010, South Koreans were at least as angry with their own government as they were with Pyongyang. When the North shelled a front-line island, killing two soldiers and two civilians, the South responded by lobbing 80 shells toward the North. Then-President Lee Myung-bak was criticized for not taking more serious action, leading to his pledge — reiterated by the current president, Park Geun-hye — to counter with greater force if provoked again.

Worries about U.S. role

One lingering concern, voiced by a minority of South Koreans, is whether the United States can act as a sufficient deterrent to the North at a time of defense budget cuts in Washington and major crises in the Middle East. The United States has tried to assuage those worries, and deter the North, by flying the stealth bombers over the peninsula and speeding up the deployment of a missile-­defense system to Guam.

On Thursday, Pyongyang accused the United States of trying to bring down North Korea’s “dignified social system.”

South Korean analysts say they are most concerned about how either side can step back from the possibility of a confrontation over the next few months. The Obama administration has shown little interest in talking directly with the North, and the North is seen as having little interest in toning down its rhetoric — unless it can win some kind of concession.

“If the U.S. doesn’t want to engage, that pushes North Korea even further” to provoke, said Kim Dong-sik, a researcher at the Institute for National Security Strategy in Seoul. “I don’t know how that scenario ends.”

Yoonjung Seo contributed to this report.