A television advertising campaign spruiking the virtues of the controversial $17 billion WestConnex motorway is set to run through the 2019 state election, and has already cost taxpayers almost $2 million.

The animated campaign, which began in recent weeks, says Sydney "is made up of many different places, but they've never been properly connected".

"WestConnex is the missing piece of the puzzle that will bring Sydney closer together," it says.

The ad emphasises that there will be "more than 30 kilometres of new roads – but most of it you'll never see because it will be underground".