The BBC's Andrew Wood: The Moonie business empire appears to be troubled

The event is organised by the Unification Church, whose followers are often called Moonies, after their leader Sun Yung Moon.

The Reverend Moon is officiating at Sunday's ceremony in Seoul's Olympic Stadium. But similar mass weddings will take place simultaneously in 185 countries.

Reverend Moon plans to marry couples via the Internet and satellite

The church says 360 million couples will join in the proceedings by satellite and via the Internet, although it admits this figure is impossible to verify.

Many of those taking part only met their spouse a few days ago as is common in Moonie weddings.

Only about a third of the 40,000 couples in Seoul are actually getting married. The others are there to be blessed and to publicly restate their vows and commitment to sexual purity and fidelity.

Brainwashing accusations

The Reverend Moon has recently returned to Korea after living in Brazil, where he has been trying to build what he calls a new Garden of Eden.

Many couples have not met before they wed

He founded the Unification Church in Korea in1954 before moving it to the United States where he dramatically expanded the movement by promoting strict family values.

But the church is said to be losing support in Europe, dogged by accusations of brainwashing recruits and breaking up families.

And its business empire in South Korea is crumbling because of the country's economic crisis.