Military training was suspended, flights rescheduled and emergency calls reserved for latecomers as hundreds of thousands of South Korean students sat a crucial college entrance examination.

As every year, the focus of the education-obsessed country narrowed for one day to ensure the smooth running of the exam, seen as a defining moment that can hold the key to everything, from future careers to marriage prospects.

Police cars and motorbikes in cities across South Korea were put on standby, available for any students needing to make a late dash to take their seats before the exam began Thursday at 8:40 am.

In one case, police responded to a distress call from a father whose car had blown a tyre and hit a railing as he was driving his 18-year-old daughter to the test in the southern city of Busan.

The police took the student to a nearby hospital for treatment before rushing her to the exam centre, Seoul's CBS radio said.

More than 668,500 students took the day-long standardised College Scholastic Ability Test at 1,191 centres nationwide, the education ministry said.

Aviation authorities said 83 flights had been rescheduled to avoid noisy landings and take-offs during language listening tests in the morning and afternoon.

The stock market's opening and closing was delayed by an hour while many government offices and private companies opened late to ease rush-hour traffic so that students could arrive at test centres on time.

In South Korea's hyper-competitive education system, high marks in the exam are essential for entry to top universities, which is in turn crucial to securing prestigious jobs.

News networks offered recipes for special lunches which are easily digestible and contain ingredients supposed to boost mental concentration.

Parents gathered in anxious groups outside the test centres or went to pray for their childrens' success in Buddhist temples and churches.

The pressure on teenagers to perform well in exams is blamed for dozens of suicides every year that generally peak around the time of the annual entrance exam.

For most of their school lives, South Korean students study late into the night -- often at costly, private cram schools -- to stay ahead in the rat race for admission to top universities.

(Read by Brian Salter. Brian Salter is a journalist at the China Daily Website.)

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(Agencies)