A taxi driver who indecently assaulted an unconscious passenger during a trip in "sinister" circumstances has been jailed for nine months.

A Melbourne magistrate found Umad Siddique – who covered an on-board security camera during the 51-minute journey – assaulted the woman by touching her breast and then between her legs.

The magistrate Andrew Capell told Siddique, 29, on Monday he had taken advantage of "totally vulnerable" person and had abused the trust she placed in him as her driver.

Mr Capell also said Siddique's actions had undermined the message that people out late at night without public transport "should trust the person we get into a taxi with".

In jailing him for nine months, he told Siddique it was appropriate to send a message to like-minded others that such a serious breach of trust "will be treated harshly by the courts".