Apollo Hospital said Rajinikanth is being monitored closely and medications to control his blood pressure are being carefully titrated.
The 70-year-old would undergo further investigations on Saturday. The actor's daughter is with him.
"He is stable and is resting. Family and treating doctors have requested all well-wishers to avoid visiting the hospital as he is not being allowed to meet any visitors," the hospital said.
The actor was shooting for Tamil film "Annaatthe" in Hyderabad for the last 10 days.
A couple of people on the film sets had tested positive for Covid-19. Rajinikanth was tested on December 22 for Covid but was negative. Since then, he isolated himself and was being monitored closely, the hospital said.
"Though he did not have any symptoms of Covid-19, his blood pressure showed severe fluctuations and needed further evaluation for which he has been admitted to the hospital," the hospital had said in a statement earlier.
"He will be investigated and monitored closely in the hospital till his blood pressure settles down before being discharged. Apart from fluctuating blood pressure and exhaustion, he does not have any other symptoms and is hemodynamically stable," the statement added.
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Telangana Governor Tamilisai Soundararajan called and spoke to the doctors and wished him a speedy recovery