OSLO — Late on Friday night, a couple hundred people were packed into a dimly lit, stylishly decorated bar in the heart of Oslo’s downtown night-life district.

The place already was generating considerable buzz. It had been open for only a week, but one recent night the line to enter had snaked down the block. Inside, it felt like so many of the other hip spots in downtown Oslo — candlelight illuminating framed artwork on the walls, conversation humming over the clink of beer glasses — except for one small detail: the chess games happening at every table and countertop.

“That’s the Magnus Effect,” said Martin Mortensen, a 32-year-old software developer at the bar, referring to the Norwegian world champion Magnus Carlsen. “Almost everyone in Norway has some relationship to chess nowadays. It’s on T.V. and in newspapers all the time.”

He scanned the overflowing room. “It’s bizarre.”

Carlsen, 27, has been the world’s top-ranked chess player for the past eight years. He has won the past three world championships, and this month in London he has been locked in tense competition with Fabiano Caruana, a 26-year-old American, in a bid to claim a fourth title.