Their “immortal exploits” will “last forever”, it proclaims, as will “the friendship forged in blood between the peoples of the People’s Republic of China and the Democratic People’s Republic of Korea”.

Nearly 70 years after Mao Zedong sent millions of soldiers to save Kim Il-sung’s troops from defeat as General Douglas MacArthur’s men marched up the peninsula, China remains the isolated, nuclear-armed North’s key diplomatic backer and main provider of trade and aid.

Now the Friendship Tower, as the monument is known, attracts growing hordes of Chinese tourists – and the renovations suggest it may also be on Xi’s itinerary.

Ordinary Chinese pay travel companies around 2,500 yuan (US$360) for a standard three-day trip, arriving overland by train in Pyongyang to tour the capital’s highlights, from the Arch of Triumph to Kim Il-sung Square.

The next day they head south to the demilitarised zone that has divided the peninsula since the two sides fought each other to a stalemate in 1953, before returning home.

“I’m very interested in North Korea and wanted to come to see what North Korea looks like,” Yu Zhi, a retiree from Anhui province visiting Pyongyang, said, adding that she had a “special feeling” for the country.

“China is very friendly with North Korea,” added her fellow traveller, a woman surnamed Jin. “We have been friends for generations.”

It was not always so. Mao – whose eldest son Mao Anying was among those killed in what China still calls the War to Resist US Aggression and Aid the DPRK – described the neighbours as “as close as lips and teeth”.

Ties then waxed and waned during the cold war, when founder Kim Il-sung was adept at playing his Soviet and Chinese allies off against each other, and his grandson, the present leader Kim Jong-un, did not visit Beijing to pay his respects for more than six years after inheriting power.

No official figures are available from authorities on either side, but Simon Cockerell, general manager of Koryo Tours, the market leader for Western visitors, said there had been “a huge increase in Chinese tourists”.

At peak times 2,000 people a day had been arriving in Pyongyang, he said. “That’s far too many because there is no infrastructure to accommodate that many tourists, so [there are] problems with train tickets, with plane tickets, hotel space.”

As a result, North Korean authorities had themselves set a 1,000-a-day cap, he added, although it was unclear whether this applied across the industry or solely to Chinese, who make up the vast majority of arrivals.

“There are issues with just hundreds of people showing up at the same time.”

But tourism is not among the sectors targeted by the UN, potentially enabling Beijing to use it as an incentive for its sometimes wayward ally.

The Chinese travel phenomenon is market-driven, rather than prompted by state order, and as well as the market offered by China’s huge population, the two countries’ border enables cheap overland journeys.

But simply enabling it to take place meant “we can infer some choices are being made” by Beijing, according to John Delury of Yonsei University in Seoul.

“We know it’s a lever they can turn on and off,” he said.

Even with the diplomatic process at a standstill, he added, “the Chinese think you have to use this window of opportunity to move things forward. There has to be a path on both sides and so something like opening up tourism is a good way to enable that.”

At the Monument to the Three Charters for Reunification on the edge of Pyongyang, where two giant stone women form an arch over a road, a secondary schoolteacher from Shanghai called Peng said: “We are both socialist countries. I feel there are more Chinese coming to visit.”