About 50 Afghan couples have tied the knot in the western city of Herat in what is believed to be the first mass marriage in the country.

The men and women were married at a ceremony attended by about 1,500 guests and paid for by the Islamic charity Comfort Aid International, an organiser said.

"These couples are mainly from poor communities and could not afford the big costs of a normal wedding," said Mahdi Haidarpour, who heads Comfort Aid International in Herat.

The event cost about $US30,000 ($A35,000), which included a $US600 ($A700) cash present for each couple, Haidarpour said.

Like most weddings in deeply conservative Afghanistan, the brides and grooms were separated for the ceremony.

Marriage is a costly affair in destitute Afghanistan, involving huge dowries, expensive gifts and lavish parties with hundreds of guests.

AFP