(Bloomberg) -- Hundreds of vehicles were stuck on a state highway in Tibet after the neighboring province of Yunnan denied entry to people traveling from the Covid hotspot, saying its quarantine system had reached capacity.

Police in Tibet’s Markam county issued an urgent notice on Tuesday asking travelers to avoid leaving the region via a highway that leads to Yunnan, as well as another that goes to Sichuan. Quarantine rooms in areas across the provincial borders are full and people had become stranded on the road leading up to the checkpoint.

The traffic jam started over the weekend after Deqin county in Yunnan tightened entry requirements due to cases spreading in Tibet. At its peak, there were several hundred cars and trucks that stretched 7 kilometers (4.3 miles), though the situation has improved as more hotel rooms were made available, said an official at the Covid command center in Deqin, who did not give her name. 

Videos shared on social media showed people set up tents between cars and trucks and were cooking meals on camping stoves. Travelers have had to endure hot summer temperatures, with some avoiding turning on their car air conditioners in order to conserve fuel, according to social media posts. 

The turmoil highlights concerns from officials that people returning from popular vacation destinations will seed further Covid outbreaks across the country, as cases surge to a three-month high on outbreaks in holiday hotspots. Tibet’s flareup in particular has sparked alarm with the rural region not as efficient at tracking the movement of infected people as other more developed cities. 

Shanghai reported that a recent infection was in a boy that had returned from Tibet’s capital, Lhasa, prompting authorities to put 1,600 people into quarantine and test more than 84,000 people they deemed were at risk from exposure.

The single infection sparked panic at an Ikea store in Shanghai, when authorities locked it down after learning a close contact of the infected boy had visited.

“As China’s key transportation hub, Shanghai is facing more pressure for preventing Covid rebound amid the summer holiday travel season,” Zhao Dandan, deputy director of Shanghai Health Commission, said at a briefing on Wednesday, adding that officials are stepping up scrutiny of returnees. 

Read more: Panic in Ikea as China Locks Down Store on Remote Covid Risk

Qinghai -- another province that neighbors Tibet -- is also seeing more infections. It reported 60 infections for Wednesday, up from 15 a day ago, with cases detected in people coming from Tibet. Other provinces, including Fujian, Hubei, Zhejiang and Hunan, have also identified infections among people who have visited Tibet, according to a healthcare-focused social media account affiliated with state-run newspaper People’s Daily.

China’s virus cases have climbed to the highest since early May, as outbreaks widen in vacation hotspots across the country. Authorities have again turned to the Covid Zero playbook of snap lockdowns and mandatory quarantine for close contacts and isolation of positive cases to try and bring the flareups under control, even as the strategy is increasingly challenged by more contagious subvariants.

Read more: Seaside Lockdown Shows Covid Zero’s Lasting Hit to China Tourism

The measures have stranded tens of thousands of tourists during peak season, and dimmed the outlook for the tourism sector as taking a vacation turns into an increasingly risky gamble.

There’s no sign of the outbreaks easing. Tibet has recorded more than 3,500 local cases in the past 10 days and several cities, including Lhasa, have gone into lockdown. Hainan reported more than 2,000 infections for Wednesday, while Xinjiang reported 271.

Read more: China’s Covid Cases Hit Three Month High Due to Hainan Outbreak

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