Marie Fourie and Cecelia Bonthuys said the Marriage Act was unconstitutional because it excluded same-sex marriages and so discriminated against gays.

The ruling does not yet legalise gay unions but is being hailed by gay campaigners as a major step forward.

South Africa's constitution allows gay couples to adopt, but not to marry.

The court said the marriage between the two women could be legally recognised if the formalities in the Marriage Act were respected.

"It's not possible for people of the same sex to be currently married due to the limitations in the current marriage formula and other regulations in the Marriage Act," said Evert Knoesen of the Lesbian and Gay Equality Project.

"We have to go ahead with legal action to fix up those somewhat more minor legal problems and we foresee that within the next 12 months or so, same-sex couples will indeed be married. The principle has been won," he told South African radio.

South Africa's post-apartheid constitution, considered one of the most liberal in the world, includes a clause making discrimination based on sexual identity illegal.