Leading South Korea club FC Seoul have apologised to fans after inadvertently substituting supporters with sex dolls during their 1-0 win over Gwangju FC on Sunday.

While the season started on May 8, fans are not yet allowed in stadiums due to the coronavirus outbreak.

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For Seoul's first home game, around 20 mannequins, many holding banners and all wearing masks, were spaced evenly around the seats behind the goal usually occupied by the club's most active fans.

As the game progressed, however, Korean social media started to light up as it became apparent to viewers that these mannequins, supplied by a local company Dalkom whose CEO is a Seoul fan, looked very much like sex dolls.

In addition, some mannequins held signs offering messages of support to players and the team that seemed to reference adult content streaming sites.

Seoul said there had been a misunderstanding with the supplier and it had been told the dolls were not for adult use.

"We would like to apologise to the fans," the club said in a statement released on social media.

"We are very sorry about the supporting mannequins that were placed during the game on May 17. These mannequins may have been made to look and feel like real humans but they are not for sexual use -- as confirmed by the manufacturer from the beginning."

The manufacturer's homepage is currently offline.

"Our intention was to do something lighthearted in these difficult times. We will think hard about what we need to do to ensure that something like this never happens again," the club added.

K-League regulations forbid inappropriate or sexual advertisements with Seoul facing a hefty fine if they are found guilty.

An unnamed K-League official told news site OSEN that the matter would be looked into.

"It is not easy to say whether this breaks the rules as it is not a clear violation," the official said. "We are trying to get a clear interpretation."

With South Korea enjoying unprecedented international attention after becoming the first major league to play competitive games since the spread of the coronavirus, the club has been heavily criticised on social media with fans accusing Seoul of damaging the prestige of Korean football -- also a punishable offence.