The blackout started at about 7pm. At 7:50 limited power became available, but it is not clear when full power will be restored.
Mobile phone systems have been hit by massive traffic as people tried to find out how widespread the blackout was, and are still not back to normal.
Phuket International Airport, however, operated normally throughout.
The reasons and the site of the problem are by no means clear, with Thai PBS TV news reporting at 8:30 that the problem was in Prachuab Khiri Khan. It gave no more details.