More than half a million students in South Korea sat the crucial national university entrance exam Thursday, with authorities taking extraordinary measures, including halting flights, to minimise distractions.

The nine-hour test, which was taken by 504,588 pupils this year, is crucial for securing spots in top universities. It is also considered key to elevated social status, lucrative careers, and even marriage prospects.

Enormous pressure placed on students in South Korea's ultra-competitive education system has been blamed for teenage depression and suicide rates that are among the highest in the world.

"I'm nervous and trembling because what I've been studying for three years ends with this exam today," Lee Min-yup told AFP before going to take the test at Kyungbock High School in central Seoul.

The importance of the test was reflected by the aggressive measures authorities were taking to prevent any disturbance.

To reduce noise disruption during the listening portion of the English test, Seoul's transportation ministry imposed a nationwide ban on all aircraft takeoffs and landings outside of emergency situations.

The ban was implemented for a duration of 35 minutes, from 1:05 pm to 1:40 pm local time (0405 to 0440 GMT).

With the exception of aircraft in distress, all airborne planes were required to maintain an altitude higher than 3,000 metres (10,000 feet) during the restricted time.

More than 90 flights had to be rescheduled because of the exam.

Public offices and major businesses were requested to adjust their opening hours to 10:00 am or later to alleviate traffic congestion and ensure that students arrived on time for the nationwide exam, which started at 8:40 am.

The stock market also opened an hour later than usual.

Police cars and regional government officials were on standby to help students running late for the exam reach their test sites in time.

This year's test also marked the first time that test-takers were allowed to take the exam without wearing masks since the pandemic began.

Those with suspected Covid symptoms were still permitted to take the exam, but were asked to wear masks and have their lunches in designated separate areas.

- 'Killer questions' -

Outside Kyungbock High School early Thursday, some test-takers appeared visibly nervous, with others running late for the exam arriving on motorcycles that had been designated as emergency convoy vehicles by the authorities.

High school freshmen and juniors gathered outside the entrance of the venue to show their support.

They chanted phrases including "Success in Suneung", using the local name for the exam, while waving banners adorned with messages such as "Strive for a perfect score in Suneung".

"Since I'm not the one taking the exam today, I can smile like this, but I think next year I'll have a somewhat sad expression," Lee Dong-yun, a high school student who came out to cheer for the exam-takers, said.

Relatives also showed up to express their support for their children, with some even bringing their dogs along. Images from local media showed exam-takers kissing their pets before entering the venue.

"Right now, for them this is everything," Lee Jong-hwa, mother of one of the exam-takers, said.

"At this moment it's too much of a burden for them", she added.

For this year's exam, authorities dropped so-called "killer questions" -- which cannot be answered by simply studying the curriculum taught at public schools -- in a bid to reduce reliance on expensive private cram schools.

"In accordance with the Ministry of Education's measures to reduce private education, so-called 'killer questions' were excluded," Jeong Moon-seong, a university professor who supervised the exam's administration this year, told reporters Thursday morning.

"Questions of suitable difficulty were selected evenly to ensure that (students) can demonstrate their understanding based solely on the content covered in the public education curriculum," he added.

South Korean households spent more than $20 billion on private education for primary, middle and high school students last year, according to Statistics Korea.

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