The road was shut in both directions at 8pm last night and will remain closed until 6am on Monday as work goes on to dismantle a footbridge where the new "missing" junction 2 is being constructed at Bartle near Preston.
Work went on through the night to begin demolition of the concrete structure which straddles both carriageways.
The motorway is closed along its entire length in both directions between Broughton and Blackpool.
Detours are in place on A-roads to take traffic around the closure, with Blackpool Road in Preston and the A583 on to Blackpool expected to be the busiest.
By mid-morning today there were no reports of major hold-ups, although there was some congestion on the A585 between Kirkham and Great Eccleston.
But by lunchtime here were hold-ups on Blackpool Road along most of its length and also along the A583 Riversway from Watery Lane, past the docks to Blackpool Road.
There were also reports of congestion on the A583 near Kirkham.