The best source I can find on the subject is Combined Fleet. Once the war started, the US and Japan agreed to exchange their respective diplomatic missions, the ambassadors and their staffs, along with several foreign nationals in each nation. For the swap the two decided to use a Japanese and Swedish liner (an Italian repatriation ship is also mentioned, and the Swiss negotiated a similar action for Britain) with extensive markings to prevent attack and meet in modern Mozambique on the east coast of Africa. The Japanese Asama Maru left Japan with the American diplomatic staff and after stops in Hong Kong, Saigon, and Singapore arrived in Mozambique on 22 July 1942. Likewise the Swedish liner Gripsholm before sailing to Brazil for more passengers, arriving in Mozambique later on the 22. The actual exchange took place the next day, where passengers left one ship and boarded the other, and each ship returned to their port of origin.

The article covers other diplomatic transfers and adds more detail and the respective Tabular Records of Movement add even more. It’s an interesting read.