South Korean police have detained a man suspected of stabbing a high school teacher with a knife in the city of Daejeon.

The stabbing follows a separate, apparently random attack on Thursday in which 14 people were wounded near a busy subway station in Seongnam.

Officials at the Daejeon Metropolitan Police Agency did not immediately release the personal details of the suspect in the Friday morning attack on the teacher at Songchon High School, describing him only as a “man in his 20s or 30s”.

According to police, the suspect waited for the teacher to step out of a classroom before stabbing him and fleeing the scene, which, according to officials, suggests they were acquaintances.

Police and fire department authorities did not specify the teacher’s health condition.

The attack in Daejeon, about 120 kilometres (75 miles) south of Seongnam, came hours after President Yoon Suk Yeol called for “ultra-strong” law enforcement measures to restore faith in public safety after Thursday’s violence, which he described as a “terrorist attack on innocent citizens”.

At least two people were in life-threatening conditions after Thursday’s attack in Seongnam, in which a car rammed on to a pavement before the driver stepped out and began stabbing people at random at a shopping centre linked to the Seohyeon subway station at the heart of a bustling leisure and business district.

Of the five people who were hurt by the car, at least two were admitted to hospital in a critical condition.

Among the nine who were stabbed, eight were being treated for serious injuries, according to Gyeonggi Province fire department officials.

Police are questioning the 22-year-old suspect.

They did not identify the suspect or offer any immediate information about a potential motive.

During police interviews, the suspect talked incoherently and said he was being stalked by an unspecified source, said Park Gyeong-won, an official at Gyeonggi’s Bundang district police station.

The suspect purchased the two knives he used in the stabbings from a different shopping centre on Wednesday, Park said, but there is not clear evidence he planned the attack in advance.

Photos from the scene showed forensic units examining the halls of the AK Plaza, where the attack took place on Thursday.

A white Kia hatchback with a broken front window and ruptured front tyre could be seen on a pavement near the subway station.

A witness named Hwang Hee-woon told YTN television that he “heard a sound from the first floor that seemed like a scream, so customers and shop workers were gathering on the rails of the second floor near the escalator to see what was happening below”.

“Suddenly, someone told us the person who committed the crime was coming up to the second floor, so we ran away in panic,” he said.

He ended up hiding inside a refrigerated storage room with some shopping centre employees.

Thursday’s attack was the country’s second mass stabbing case involving random targets in a month.

In July, a knife-wielding man stabbed at least four pedestrians on a street in the capital Seoul, killing one person.

Attacks by firearms are rare in South Korea, which tightly controls gun possession, but there are not meaningful restrictions applying to knives, including kitchen tools that are often used for attacks.

In response to Thursday’s attack, Mr Yoon called for closer monitoring of social media to detect threats, deploying more law enforcement officers for prevention and equipping them with better suppression gear, according to Seoul’s presidential office.

In response to the president’s comments, National Police Agency Commissioner General Yoon Hee-keun declared in a televised statement the start of an indefinite “special surveillance” period, during which police officers will step up patrols and stop-and-search activities to guard against “people suspected of carrying weapons or acting abnormally”.

Mr Yoon said police officers will also be instructed to actively use firearms or Taser guns to suppress suspects when violent crimes occur.