The failure of an unidentified piece of hardware involved in biometric processing brought the entire Consular Consolidated Database system to a halt.
The system is responsible for processing and issuing an estimated 50,000 U.S. visas per day. Applications made after May 26 were affected.
"The database has been rebuilt and is being tested," said John Kirby, State Department spokesman, at a briefing on Tuesday.
About two thirds of visa issuance facilities are back online and have been issuing visas although only 45,000 were handed out on Monday. Of those, 15,000 were issued in Beijing, which is the busiest U.S. consulate anywhere in the world.
"Significant additional numbers will be issued as the backlog clears," he said. "Many posts are now rescheduling interviews, in many cases as early as the 24th."
The State Department hasn't provided details on what exactly went wrong and why it took so long to fix, beyond saying the database needed to be rebuilt. It has stated the failure was related to a hardware device and was not the result of a cyberattack.
The same database failed at about the same time last year, throwing summer travel plans in chaos for around 200,000 people.
On that occasional, a bug-ridden software patch from Oracle and Microsoft caused the problem.
Kirby cautioned that the system was still being tested and as such could still be taken offline again.
"So far, it's going well," he said.
Throughout the outage, which also affected issuance of U.S. passports at missions overseas, the U.S. has been handling a small number of visa cases. It has issued around 1,250 visas to temporary or seasonal workers from Mexico whose biometric details were already in the system and it has handed out around 3,000 visas related to urgent or humanitarian purposes.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com