The bridge, one of the busiest in Blackpool, is due to be replaced, with partial road closures initially set to happen from next Monday.
But one lane heading over the bridge, along Plymouth Road towards the roundabout, was closed on Monday, and the footpath was closed in the same direction yesterday.
A council spokesman said: “The work wasn’t meant to start until July 4, however the contractors found some unforeseen extra work that needed doing in advance in order to make sure that they could get the temporary bridge up and open in the meantime.
“They are now on site as per the working practices in the press release from last month.”
The rebuild will cost around £6.1 million, and is needed because steelwork on the bridge, next to Layton railway station, is rotting and no longer fit for purpose.
Council chiefs say two-way traffic will be maintained at all times, before the bridge is fully closed to traffic and demolished from November 7, when the Illuminations come to an end.
The structure will be replaced by a heightened bridge so Network Rail can install overhead equipment to allow for the electrification of the train line between Blackpool North and Preston.