Chinese media said it may have been prompted by one person with COVID who visited the park from the nearby city of Hangzhou on Saturday.
Fireworks went off as health workers carried out the mass testing on Sunday night – and people had to wait for hours for a negative test before they could leave.
The park said all 33,863 people who visited over the weekend had tested negative.
However, they must get tested again and have their health monitored.
One visitor, who gave her name as Chen, said she was in the park when an announcement was made at about 5pm that everyone had to get tested.
“No-one complained, and everyone behaved really well,” she said.
Disneyland said the park would stay closed on Monday and Tuesday to comply with health rules.
The shutdown shows the tough measures in place in China as it enforces a zero-tolerance approach in an attempt to stamp out any local outbreaks.