Credit cards and debit cards cannot be used and bank staff are now deployed outside branches, telling customers that they cannot use the ATMs, nor be served inside the banking hall.
The crash also affects anyone trying to access KTB accounts from ATMs in other countries.
This is the second time this year that the KTB system has crashed. The first was on March 10 when a power failure knocked it out at 8:30 am. It took three and a half hours to completely restore the system.
Attempts to reach the bank for comment or explanation have so far been unsuccessful, with the call centre number, 1551, constantly busy.