Travel agents in the Chinese city say they have seen a surge of interest from across the country in recent weeks, boosting an already strong peak tourism season.

North Korean leader Kim Jong-un's economic reform plans and warming ties between Pyongyang and its main backers in Beijing are behind the jump in activity, agents say.

"People who may have long been curious about seeing North Korea may think that now it is safer than ever," said tour guide Teng Yi, who returned from leading a tour to Pyongyang on Sunday.

After meeting with Chinese President Xi Jinping in Beijing on June 19, their third such summit since March, Kim spent the subsequent month inspecting factories and industrial projects along the Chinese border region.

The unusually long trip, plus meetings with US Secretary of State Mike Pompeo and South Korea's unification minister, underlined Kim's desire to rally support at home for his economic drive and convincing outsiders of his willingness to denuclearise.

A dip in visitors after a tour bus crash killed 32 Chinese nationals in April proved a mere blip. Half-day and one-day tours to the neighbouring North Korean city of Sinuiju now book out within an hour of tickets being released, travel agents in Dandong say.

Four-day tours, which take in the capital Pyongyang and the Panmunjom truce village are fully booked through to the end of August, despite increased capacity through more frequent trains and coaches.

Tourism is one of the few remaining reliable sources of foreign income for North Korea, after the UN imposed sanctions targeting 90 per cent of its $US3 billion annual exports including commodities, textiles and seafood.

China has not provided a breakdown of the number of tourists travelling to North Korea since 2013.

The Korea Maritime Institute, a South Korean think-tank, estimates tourism generates $US44 million a year for the isolated country, with Chinese tourists making up about 80 per cent of all foreign visitors to the North.

Australian Associated Press