SEOUL, South Korea -- South Korea closed its airspace to ensure silence and offered police escorts for tardy test takers Thursday as more than half a million students sat high-stakes college admission exams.

Seoul's Education Ministry said 508,030 students were sitting the annual nine-hour test this year, the results of which are crucial for securing spots at top universities.

But the bevvy of anxious parents dropping off their children for the test -- and visiting local temples to pray for success -- highlights the broader significance of the exam, success in which is also seen as the key to lucrative careers and even marriage prospects.

The enormous pressure 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.

This year's exam, locally known as "Suneung" -- an abbreviation for College Scholastic Ability Test -- marks the third year it has been held under Covid-19 restrictions.

Pandemic-linked measures continue to affect the students, who will have to bring their own water and lunch and be masked throughout the test, which kicked off at 8:40 am local time (2340 GMT).

At lunchtime, students taking the exams will be given a three-sided screen to shield them from others as part of a Covid-prevention measure, and they are banned from chatting or eating in groups.

Local police were called in to transport students running late to enter classrooms by a 8:10 am deadline either on motor bikes or in police cars, as has happened in previous years.

Videos of the police rushing students to exam halls have been an annual ritual for domestic media, though some local authorities this year banned the transport on motorcycles, citing safety issues.

National importance

At the Ewha Girls' Foreign Language High School in central Seoul, some test-takers arrived holding hands with their visibly nervous parents.

One student got out of a police vehicle and rushed to her classroom, seemingly desperate to make it on time.

Among this year's half a million exam takers, 2,400 have tested positive for Covid-19, according to the education ministry, and will sit their exams in specially designated test centres and medical facilities.

The national importance of the exam is reflected in the extraordinary measures South Korean authorities take to remove any disturbance that could hinder students.

Public offices, banks and the stock market open an hour later than usual to help ease traffic congestion and ensure students arrive on time for the exam.

All take-offs and landings at the country's airports are suspended for 35 minutes during an English listening test from 1:05 pm except for emergency landings. All planes in the air must maintain altitude higher than 3,000 metres (10,000 feet).

The South Korean transport ministry said 77 flights -- 18 of them international -- have been rescheduled because of the exam.