The police teams are searching Imamoglu's residence, the Sozcu Daily newspaper reported.
"Hundreds of police have gathered at my doorstep. We are facing a great tyranny. I entrust myself to the nation," said Imamoglu from his residence in a video posted on X.
Meanwhile, Imamoglu's press advisor Murat Ongun was also detained, Ongun said in his statement on X.
The cause of the detentions was not immediately clear, Xinhua reported.
Imamoglu's undergraduate diploma was annulled on Tuesday as part of an investigation initiated by the Istanbul Chief Public Prosecutor's Office following reports alleging that his diploma was fake.
In February, the mayor officially applied to his Republican People's Party (CHP) to become the opposition party's presidential candidate. CHP is expected to announce its presidential candidate at its congress on Sunday following a vote by party members.