Police in Northern Ireland are concerned for the welfare of missing 30-year-old Xiaofang Ni and Zhiling Ni, 26, last seen at the Giant's Causeway in Co Antrim.
Both women failed to return to their tour bus whilst visiting the site on 29 July.
Xiaofang Ni is described as being around 1.5m (5'2") tall, of slim build.
When last seen she was wearing a yellow jumper, blue jeans and flip flops, with short black hair.
Zhiling Ni is also around 1.5m (5'2") tall, of slim build, and was wearing a pink jumper, blue jeans and flip flops.
Police have appealed to anyone who knows of their whereabouts to contact them on the non-emergency number 101.