South Korean President Yoon Suk Yeol called on Friday for mobilising all possible forces and police announced they "won't hesitate" to use their firearms after a series of stabbings shook the typically low-crime country.

The second mass stabbing in two weeks took place Thursday in Bundang, about 20 kilometres (12 miles) southeast of Seoul, when an attacker drove a car into a pedestrian walkway before attacking people at a department store, police said.

At least two people remain in critical condition, authorities said, while copycat threats were posted online hours after the incident.

"The indiscriminate knife-wielding attack at Seohyeon Station is an act of terrorism against innocent citizens," Yoon said in a statement released by his office.

"The government must mobilise all police forces to make sure the public does not feel anxious," he said, adding that threatening messages had also appeared on social media.

Hours after the president's remarks, a high school teacher was reportedly attacked with a knife in Daejeon, around 139 kilometres south of Seoul.

The two attacks follow an incident on July 21, when one person was killed and three wounded in another stabbing in the South Korean capital.

Calling the situation "an urgent emergency", police announced the launch of a "special security initiative" to address knife-related violence and prevent copycat crimes.

"We will maximise the use of police forces, such as local police, riot police units and detectives," Yoon Hee-keun, commissioner general of the National Police Agency, told reporters on Friday.

Police -- who are allowed to carry guns but typically are extremely reluctant to use them -- will not "hesitate to use legitimate police force such as firearms and Tasers" when it comes to knife-wielding crimes, he said.

Police will also "actively apply immunity provisions for law enforcement" based on prioritising public safety, he said.

"Selective searches and questioning will be conducted, following legal procedures, for suspects carrying knives or exhibiting unusual behaviour," he added. "We ask for the public's understanding and full cooperation."

Also on Friday, Seoul's justice ministry said it was reviewing a proposal to introduce a "non-parolable life sentence" in the criminal law as a response to such heinous crimes.

South Korea is generally a very safe country, with a murder rate of 1.3 per 100,000 people in 2021, as per official statistics.

By contrast, the global average is six homicide deaths per 100,000 people, according to the World Health Organization.

But the recent incidents in South Korea have triggered concern online.

"I've suggested to my mom that she carry something for self-defense, but it still makes me feel uneasy," one wrote on Twitter, which is being rebranded as X.