Premier Gladys Berejiklian says the massive WestConnex spaghetti junction being built at St Peters will "give life" to Sydney's inner west as construction on the interchange forged ahead.

But opponents of the highly contentious 33-kilometre motorway project have criticised plans for green space beneath the interchange as creating "the world's worst park".

The St Peters spaghetti junction. Credit:NSW Government

Ms Berejiklian and WestConnex Minister Stuart Ayres continued to spruik the benefits of the $16.8 billion mega toll road as they offered a glimpse of above-ground construction at the interchange.

The road and tunnel network for WestConnex, described as the nation's largest infrastructure project, is aimed at linking Sydney's existing motorway network and easing congestion.