The event, inscribed onto Unesco's list of intangible heritage last year, begun at exactly 4am on Monday with the so-called Morgestraich parade during which participants headed through the streets holding lanterns showing topical subjects.
Targets of the satire that marks the Basel event this year included North Korean Supreme Leader Kim Jong-um and, for the second-year running, US President Donald Trump.
The unique festival lasting exactly 72 hours will end at 4am on Thursday so there is still time to join in the fun if you are in the vicinity.
Here are a selection of the best images so far:
A lantern depicting North Korean leader Kim Jong-un and Donald Trump on Monday. Photo: AFP
Another image from Monday's Morgestraich parade. Photo: AFP
"Mum, where are you?"
I love experiencing local traditions! Yesterday, it was so fun to take part in Basel's Fasnacht.— Laura Vitiello (@flyaway2anthrpl) February 20, 2018
So much work must go into making these masks!
::::::::::#basel #swisstourism #fasnachtbasel pic.twitter.com/cqmPZN1JiQ
"Stepping on confettit all day at the Basel carnival"