About $1.8 billion of property acquisitions have almost been completed for the second stage of Sydney's new metro rail line as work begins on demolishing the first towers in the central city to allow for construction of new train stations.

About 60 per cent of the money spent on acquisitions has been in the CBD where demolition of the first major high rise – the 17-storey building at 55 Hunter Street – will begin within the next few months.

It is one of five towers to face the wrecking ball at Martin Place for the new train station for the second stage of the $20 billion metro line from Chatswood in the city's north to Sydenham in the south, and onto Bankstown in the west.

One of the others is the 22-storey tower at 39 Martin Place, home to high-end jeweller Tiffany & Co and a law firm, which will be knocked down next year. A childcare centre in the tower will close its doors next week.