From 1995 to 2012, the annual number of tourists going to Japan increased from 3.3 million to 8.4 million, a growth rate of about 6% each year.

And then, the deluge.

In its most recent report, the United Nations World Tourism Organization (UNWTO) estimates that about 28.7 million tourists visited Japan in 2017. This increase, a change of more than 20 million over just five years, is the largest ever recorded by the organization, which keeps statistics going back to 1995. The UNWTO considers any overnight stay by a foreigner a tourist visit.

It is likely the largest increase in tourists, in absolute numbers, a country has ever seen. While it is possible there was a larger increase somewhere before 1995, tourism levels were much lower before this period. The total number of global tourist visits in 1995 was about half a billion; in 2017, it was over 1.3 billion.

Although international tourism is growing across the world, what is happening in Japan is special. Between 2012 and 2017, the number of international tourist visits to Japan increased by a whopping 250%, far more than other countries.

Japan’s tourism boom stems from a relaxation of visa requirements, particular for visitors from China. It has also been spurred by the fall in the value of the yen starting in 2011. This made the historically expensive country more accessible for middle-income travelers. Although Chinese tourists make up the biggest share of the growth, more tourists are arriving in Japan from nearly everywhere.

The increase has been a boon for Japan’s economy, but not everybody is happy about it. The Japan Times reports that in cities like Kyoto and Osaka, which have seen the greatest influx of tourists, some locals feel that their cities have become overrun. The Japanese media calls the the phenomenon “tourism pollution.”

The tourism tide doesn’t seem likely to turn anytime soon. Japanese prime minister Shinzo Abe is targeting 40 million tourists in 2020 when the country hosts the Olympics. Recent trends suggest that number is well within reach.