The reports came after transitional forces claimed control of Sirte, Col Gaddafi’s birthplace, following weeks of fierce fighting.
Col Gaddafi is said to be wounded. There is no independent confirmation of the reports.
The colonel was toppled in August after 42 years in power. The International Criminal Court is seeking his arrest.
“He’s captured. He’s wounded in both legs,” National Transitional Council (NTC) official Abdel Majid told Reuters news agency.
“He’s been taken away by ambulance.”
AFP news agency quoted another NTC official, Mohamed Leith, as saying that Col Gaddafi had been captured in Sirte and was “seriously wounded” but still breathing.
A soldier who says he captured Muammar Gaddafi tod the BBC the colonel had shouted: “Don’t shoot!”
The BBC’s Caroline Hawley in Tripoli says although the capture is unconfirmed, ships and cars have been sounding their horns in the capital and guns are being fired in celebration.