Updated

Looters broke into a Nile-side luxury hotel in the Egyptian capital early Tuesday, taking advantage of clashes in the streets outside to trash shops and the lobby before police and demonstrators alerted via social media drove them out, a hotel spokeswoman said.

The break in, which happened despite the presence of hundreds of riot police nearby, cast another cloud over Egypt's flagging tourism industry. Once a key source of foreign revenue, tourism has been hard hit by waves of political turmoil and street violence that have dogged the country since the uprising that toppled longtime autocrat Hosni Mubarak in 2011.

Egypt's latest unrest erupted around Friday's second anniversary of the revolt, and the Semiramis InterContinental, which overlooks Cairo's landmark Tahrir Square, has been on front line of clashes between riot police and rock-throwing youths since then.

Around 2 a.m. on Tuesday, dozens of people forced their way into the hotel, sacking stores inside its shopping plaza and smashing glass and furniture in the lobby.

"Looters had tried several times to break in over the past two days, but when protesters beat back police on Monday night they operated with impunity," said Nabila Samak, a spokeswoman for the hotel.

When appeals to police failed to end the incursion, Samak said she started contacting journalists and calling for help on social media.

"We r under attack and several thugs have entered the Semiramis ... We need help," she wrote on the hotel's Twitter account in the first of several pleas.

Help finally arrived in the form of security forces and protesters, who drove the looters out about two hours after they broke in, she said.

On Tuesday, broken glass, fallen chandeliers, and papers lay scattered across the lobby, and the sting of tear gas still hung in the air. Workers wearing surgical masks swept up the debris as men welded steel plates to block the main entrance to the hotel, which is now closed.

Security officials who declined to be named because they were not authorized to brief reporters said police had foiled an attempted robbery by 12 masked gunmen they suspect were criminals using the street clashes as cover. AP television footage shows protesters trying to arrest some of the thieves.

Once an opulent stomping ground for elites in the first half of the 20th century, the Semiramis and neighboring Shepheard Hotel have both been rebuilt since and now rely heavily on foreign tourists.

Outside the Semiramis on Tuesday, riot police guarded the main entrance but street battles showed no signs of abating as fire bombs and tear gas canisters traced arcs in the sky. The nearby U.S. Embassy suspended public services.

The fresh wave of unrest roiling Egypt is likely to further stifle tourism, which has traditionally been one of the country's main economic pillars -- along with revenues from fossil fuel sales and the Suez Canal.

From January through November 2012, 10.5 million tourists brought some $9.37 billion to Egypt, Tourism Minister Hesham Zazoua said in December, when he expected total annual tourist numbers to reach 11.5 million. But December figures, yet to be announced, will likely bear the impact of the recent violence.

The numbers pale in comparison to pre-revolt levels. In 2010, 14.7 million tourists brought in some $12 billion in revenue.