The deputy governor of Shabwa, the province where the abduction took place a day earlier, said he expected the five Germans to be freed later Thursday.
"The negotiations are progressing well and we expect them to be released in the coming hours," Nasser Ba'oum told The Associated Press.
Armed tribesmen kidnapped former Deputy Foreign Minister Juergen Chrobog, his wife and three children as they were touring the mountains of eastern Yemen on Wednesday. The tribesmen stopped the Germans' two cars, forced them into the kidnappers' vehicles and sped off.
The kidnappers are demanding that the Yemeni government release five detained members of their al-Abdullah bin Dahha tribe who are on trial for allegedly killing two members of a rival trial in October.
The German Foreign Ministry said Thursday it was "confident that the kidnapping can be brought to a good end."
But ministry spokesman Martin Jaeger said it was "unhelpful" to predict when the hostages will be freed.
The tour operator engaged by the Chrobog family said Thursday it had contacted the hostages through the mobile phone of their tour guide who was seized with them.
"We spoke with the family ... at 8 a.m. today our time, and they are well," Mohammed Abdulkarim Abu Taleb told Germany's ARD television. "We have learned that these negotiations have just started with the kidnappers and the negotiators who were sent by the Interior Ministry."
Along with the Interior Ministry negotiators, elders from other tribes in the area were involved in talks with the kidnappers.
The leading tribal mediator, Awadh bin el-Wazeer, said the kidnappers have proposed several options to end the kidnapping: arrest and put on trial five from the rival tribe, release the five bin Dahha tribesmen currently on trial and settle the matter according to tribal traditions or hold their trial outside Shabwa,
Bin el-Wazeer said talks with the kidnappers should not take long and said he was optimistic of the Germans' release. But he did not specify a timeframe.
Tribesmen frequently kidnap tourists in an attempt to force concessions from the government in Yemen, a poor, mountainous nation on the southern tip of the Arabian Peninsula where state control in outlying areas is shaky.
Chrobog, 65, served as deputy foreign minister in Gerhard Schroeder's government, which left office in November. Previously he was a German ambassador to Washington.
In 2003, Chrobog headed a team that negotiated the release of 14 tourists, including nine Germans, who were kidnapped in the Sahara desert and freed six months later by their captors in Mali. His wife, Magda Gohar-Chrobog, is a translator and the daughter of an Egyptian writer, Youssef Gohar.
Hostages are usually released unharmed in Yemen, but several were killed in 2000 when security forces carried out a botched raid to free them.