Pattaya, Thailand - Lips locked at all times - including for bathroom breaks and meals - is the less than romantic challenge facing Thai couples trying for the kiss to blow away all kisses at a Valentine's Day marathon.

Seven couples have brought their lips together in the Thai beach resort of Pattaya, about 100km south-east of Bangkok, hoping to break the world record for longest continuous kiss - which currently stands at nearly two days.

The marathon kicked off on Sunday and will go through Valentine's Day, with prizes and glory for the pair that manages to hold out longer than 46 hours, 24 minutes and nine seconds.

That record was set in 2011 by Lakkana Tiranarat, 31, and her husband, both back this year for another go.

“We'll try to do better than last year but maybe just for a little longer. We'll see how tough the other competitors are but we'll do our best,” Lakkana said.

Each couple has a space of 1 square metre to prove their affection for each other.

Food and drink must be taken through a straw. Teeth brushing would also risk breaking the locked lips and result in disqualification.

The toilet is off-limits for the first three hours of the contest. After that, lips still together, they must be accompanied by a referee for any later bathroom break.

Suggesting the contest has more to do with ordeal than romance, the organisers noted that the number of contestants has fallen by half from last year's marathon.

“The world record last year of 46 hours, 24 minutes and nine seconds is very difficult to beat. Contestants have to be patient to prove their love,” said Somporn Naksuethrong, general manager of Ripley's World Pattaya.

The record-breaking couple stands to gain a diamond ring worth 100 000 baht ($3 333) and a hotel gift voucher for 200 000 baht - as well as, presumably, very sore lips.