A taxi driver has been threatened at knifepoint during a carjacking in Melbourne's south-east.

Investigators believe the driver picked up three male passengers on Bamby Grove at Cranbourne East just before 5am on Tuesday.

Police say the men, armed with a knife, made the driver get out of his car, before speeding away.

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The stolen taxi was later found dumped on Bruin Street at Clyde, about 4km away.

The 38-year-old driver was not physically injured and no arrests have been made at this stage.

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