A 2,964km section of pipeline, also opened on Monday, links Taishet in eastern Siberia with Skovorodino in the Amur region of the Russian far east near the border with China.
A second pipeline section will run another 2,100km from Skovorodino to Kozmino Bay, near Nakhodka on Russia's Pacific coast, where the oil port has been built.
Until its completion the oil will be carried there by rail.
Putin said it cost 60 billion roubles, the equivalent of about $2bn, to build the Kozmino terminal.
Transneft and Chinese oil group CNPC have signed an agreement on the construction of a 67km branch line to China which will initially carry 15 million tonnes of oil a year and is due to become operational next year.
"The pipeline's launch will strengthen Russia's energy security," Nikolai Tokarev, the president of Transneft, said.