A message on the website says it is “busier than usual” and “ you are now in a queue.”
Despite several political challenges, millions more drivers of the most polluting vehicles face daily charges of £12.50 to travel in and out of every London borough from today.
The expanded Ultra Low Emission Zone took effect at midnight.
Drivers are also being warned not to fall victim to copycat ULEZ charge websites.
Some people claim they have forked out money in alleged TfL fines, only to find the websites that have appeared in some online searches aren’t genuine.