High school students in Beijing are far more promiscuous than their teachers or parents think, according to a survey conducted in a city district.

More than half of those polled said there was nothing wrong with a one-night stand; and 6.2 percent admitted they already had a sexual encounter, according to the results released recently.

The average age when they first had sex was about 15, said the survey of 2,300 high school students in Xuanwu District . According to a 2005 survey by Durex, the condom maker, the global average age was 17.3.

The findings surprised even sex educators.

"The new generation is open-minded about sex, indeed we can only conclude that it is a result of a fast-changing society," Zhang Meimei, professor of education at Capital Normal University said.

Of the 1,300 girls asked if they would agree if their boyfriends sought sex, only six gave a definite "no".

The typical answer: "As long as he loves me, it's OK."

About 200 boys and girls said they were willing to have a one-night stand if an opportunity arose.

About 30 percent believed that teen sex is fine as long as it is consensual, and 55 percent said it depends on how much the two love each other.

Contrasting with the openness about sex is a lack of sexual knowledge.

More than 40 per cent of those who had sex didn't use contraceptives for the first time.

Teenage pregnancies have been on the rise in recent years; and under-age girls account for about a quarter of the 1.5 million abortions on the mainland each year.