The two 270-tonne form travellers were hydraulically jacked into place at the south pylon in the Mersey estuary.
The machines, which act as movable concrete formwork, are positioned 26 metres above the river bed. Workers are now making preparations to cast the first part of the bridge deck from the south pylon, which will take place in May 2016.
Three pairs of form travellers – one pair for each pylon – will be used to cast the spans between the three bridge pylons to create the 1km reinforced concrete bridge deck. This is expected to take around 12 months to complete.
The form travellers will be lifted into place at the north pylon later this month, while the machines for the central pylon will be positioned in the summer.
The Mersey Gateway bridge is on schedule to open in autumn 2017.
Halton Borough Council is the client for the project and it awarded a 30-year contract to design, build, finance and operate the project to the Merseylink Consortium in 2014. Equity partners are Macquarie Capital Group, BBGI, and FCC Construcción. The construction joint venture is made up of Kier, Samsung C&T and FCC.