Libyan military sources said the Mercedes bullet-proof cars left Libya for Algeria through the border, without any pursuit from the rebels.
The vehicles may have also carried other important Libyan officials.
An uprising against Gaddafi's 42-year rule began in February. An international military operation "to protect civilians" began March 19 following a UN resolution.
Rebel forces have got control over large swathes of the country and most of the capital, Tripoli.
The Sun earlier reported Gaddafi may have fled on a golf buggy through a network of tunnels under his palatial building in Tripoli.