An off the cuff tweet by Elon Musk has left Bulgarians over the moon, hoping the world's richest man may be planning to visit the EU's poorest region.

The Tesla, SpaceX and now Twitter boss -- who is not immune to bouts of online whimsy -- recently commented on an image of the towering Belogradchik Rocks in northwestern Bulgaria under menacing clouds.

"Pretty sure that was in Elden Ring," Musk tweeted, referring to one of his favourite video games.

Bulgarians were quick to educate him.

"Dear Elon, this is from Bulgaria! I invite you to see this place," Tourism Minister Ilin Dimitrov responded.

Hundreds of other Twitter users did likewise, delighted by the attention for a country rarely in the spotlight of the rich and famous.

An official invite was promptly dispatched, accompanied by a silver rhyton drinking horn, a symbol of the ancient Thracian civilisation that Bulgaria prides itself on.

- Mystery deepens -

The plot thickened when the chef of a high-end restaurant about 20 kilometres (12 miles) from Belogradchik published an email purportedly from SpaceX hinting at a visit by Musk in April 2023.

The whole episode ignited a social media buzz, with memes aplenty showing the billionaire drinking the local rakia alcohol or dressed in traditional Bulgarian attire.

Not everyone was star-struck. "He will come and buy our land," one woman worried.

But the online frenzy has delighted Vladislav Terziiski, who took the picture of the spectacular Belogradchik rocks and its fortress some five years ago.

"It is so rare that good news from Bulgaria sparks such interest," he told AFP, welcoming "the wave of reactions, jokes, anecdotes and expressions of national pride."

As for a possible visit by the man himself?

"I am quite sceptical," Terziiski said. "But I keep some hope in my heart."

- 'Three-day wonder' -

The Belogradchik fortress awaits its "messiah", political scientist Dimitar Ganev joked on Bulgarian television.

Almost obscured by the mist on a cold November day when AFP visited, the impressive rocks were indeed waiting... for tourists.

While visitors frequent the site in the warmer spring and summer months, the biggest group on that November day was a three-men camera crew filming for their own project.

Also, few of the 5,500 inhabitants of the little town at the foot of the fortress were getting that excited.

Like the rest of Bulgaria, whose population has been dropping since the end of communism, Belogradchik has lost half of its people since 1991.

Musk "does what he wants, why not come and visit a nice site and a poor region", said Svetoslav Zahariev, a construction worker in his 50s, who was "disappointed to find the same misery" on his return here after 16 years working abroad.

More than 40 percent of the region's people live below the poverty line, making it the EU's poorest, according to Eurostat.

Local officials are pushing concrete government policies to help develop tourism, instead of empty declarations.

"You see how one picture has reached Musk. We can't do all this alone, we need a government policy (for tourist development of the region)," longtime mayor Boris Nikolov told AFP.

Tourism numbers increased sharply after the Belogradchik Rocks were named as one of the New 7 Wonders of Nature poll by a Swiss foundation in 2007.

But people left "disappointed by the lack of infrastructure and accommodation", deputy mayor Rosen Mladenov lamented.

"What is this country that relies on a tweet from Musk to develop its tourism!" he fumed.

And even if the tech billionaire comes, he "would only be a three-day wonder, unless he invests here", Nikolov said.

So far Musk has remained uncharacteristically silent, ignoring numerous questions on Twitter from the Bulgarian media asking him to confirm or deny a visit.

Should Musk venture into this neglected corner of Bulgaria, he should not risk one of his Tesla cars on its rutted roads, a Sofia newspaper warned. Instead, it said, it was best he come in a rocket.