"He has fallen ill and got admitted. He is fine now," Chief Minister Mamata Banerjee said at the state secretariat.
Belle Vue Clinic CEO P Tondon said the minister came to the hospital at 4.30 pm for a health checkup.
"Since there are many tests to be conducted so we asked him to stay back," he said without divulging any details of his sickness.
The 68-year-old Mitra is under the supervision of Dr Naresh Goyal, general medicine and diabetes specialist.
Tondon said the minister will be released the day after tomorrow after a detailed check-up.