P.S. I've also tried to start the game without using website and login server seems to be down.
Finally GMs have posted official statement regarding the issue (2020.03.25 17:25 GMT/UTC):
We are investigating problem with official website.
If you're currently logged in the game you can continue to play the game as usual, but once you close the client you will not be able to log in again.
GMs have posted another official statement regarding the issue (2020.03.25 18:40 GMT/UTC):
Problem was resolved around 4:35 (2020.03.25 18:35 GMT/UTC). The site is back and you should be able to login.
We apologize for any inconvenience.