The iconic yellow Hato sightseeing bus is once again becoming a familiar sight in Tokyo and Yokohama thanks to a surge in domestic travelers from outside the capital.

According to Hato Bus Co., customers who toured central Tokyo climbed 9.6 percent to 934,306 in the 12 months through June — a level unseen since the late 1980s bubble economy.

Particularly popular were tours including Akasaka Palace, the neo-baroque-style Government Guesthouse that opened to the public in April last year, and the National Museum of Western Art in Ueno Park, which was designated as a World Heritage site in July 2016.

A Hato Bus official said the Tokyo 2020 Olympics will pose its "biggest opportunity" and that more tours related to the sporting extravaganza were planned.

The last time Tokyo hosted the Olympics, back in 1964, Hato Bus set a record with 1.23 million customers. After that, patronage hovered at around 800,000 in the mid-1970s before surging to 944,872 in 1989, near the bubble's peak. By 2001, however, patronage had dropped to around 520,000.

Foreign visitors comprise 10 percent of Hato Bus customers, but demand has been falling.

In fiscal 2015, foreign customers fell 5.6 percent on year to 83,879. Those who took tours offered in Chinese tumbled 24.6 percent to 15,267, probably due to more Chinese opting to explore other parts of Japan.

Domestic demand has recovered in line with a drop in Tokyo hotel rates, which had soared in recent years amid Japan's tourism boom.