The park closed Monday for testing of staff and visitors, Walt Disney Co. and the government said in separate statements. The city health bureau said guests all tested negative and were allowed to leave by 8:30 p.m.
No details of a possible outbreak were released, but 1.3 million residents of the downtown Yangpu district were ordered Friday to stay at home for virus testing.
President Xi Jinping's government is sticking to a severe "Zero COVID" strategy that has shut down Shanghai and other cities this year to isolate every case while other countries are easing anti-virus controls.
Also Tuesday, authorities in the southern territory of Macao were carrying out virus tests on all of its 700,000 residents after one case was found last week.
"Zero COVID" has kept infection rates relatively low but at a high cost as businesses struggle with repeated shutdowns.
Hong Kong’s main stock market index surged 5.2% on Tuesday after a comment circulated on Chinese social media that said the ruling Communist Party might set up a "reopening committee" to look at ways to wind down anti-virus controls.
A foreign ministry spokesman, Zhao Lijian, told reporters he was "not aware of what you just mentioned" when asked about the rumor.
Outbreaks in Shanghai in March led to a shutdown that confined most of its 25 million people to their homes for two months.
The city government appealed to anyone who had visited the Shanghai Disney Resort since Thursday to undergo three days of nucleic acid testing and avoid gathering in groups.
Disney said Monday parts of the resort closed due to anti-virus regulations but gave no indication visitors were kept inside. It said Shanghai Disneyland, Disneytown and Wishing Star Park were closed while two hotels were operating normally.
Some rides and other amusements kept operating Monday while visitors were tested, according to social media posts.
"Please return and take a tour in the park," a video on the popular Sina Weibo platform showed an employee in a mask saying to guests. "The park’s gates are all closed temporarily, and you cannot leave now."
Another video on Sina Weibo showed technicians in white protective suits who appeared to be taking throat swabs from guests after dark while police watched and a fireworks display lit up the sky behind them.
"The most beautiful nucleic acid detection point," the account user wrote.
In the central city of Zhengzhou, thousands of employees who assemble Apple Inc.'s new iPhone 14 walked away from a factory operated by Taiwan's Foxconn following outbreaks and complaints about unsafe working conditions.
Foxconn said it has implemented "closed loop management," the official term for employees living at their workplace and having no outside contact.
AP video producer Liu Zheng contributed.