Stunned visitors watched as a giant lighting rig was craned into position at a Kent tourist attraction over the weekend.
It is understood to be part of a major movie being shot at The Historic Dockyard in Chatham.
"It's certainly not for Call The Midwife – this is big budget," said one insider.
The hit BBC programme Call the Midwife has been filmed there since it began more than a decade ago, with the attraction now offering behind the scenes tours.
The Dockyard has been home to many film crews over the years, shooting scenes for Netflix's Bridgerton, the musical Les Miserables starring Russell Crowe, and both Sherlock Holmes movies featuring Robert Downey Jr and Jude Law.
Coloured lights had been set up inside the Victorian ropery, positioned to shine out of the windows. The huge lighting rig was near the entrance to the ropery building where a walk-way had been cordoned off.
The same team installing the lights is believed to behind the closure of the Kingsferry Bridge leading to the Isle of Sheppey at the end of the month.
Kent Film Office is remaining tight-lipped but it is likely to be part of production company Stinger UK which has already admitted it is shooting scenes for a "large US feature film" across the county.
Kingsferry Bridge is to be closed from 4am on Saturday, October 29, to 10pm on Sunday, October 30, weather permitting.
The Sheppey Crossing will remain open. There will be no train services to Sheerness on the Sunday.
The bridge's most recent starring role was in ITV's drama Too Close in April last year when a car was driven off the road during a dramatic £100,000 night stunt and plunged into the Swale.
A BBC crew is already on the Island finishing off location work for the popular crime drama Silent Witness starring Emilia Fox and David Caves.
The pair, who play forensic pathology experts Dr Nikki Alexander and Jack Hodgson, have been filming across the Island but most work has taken place in a house on The Leas at Minster.
Cyclist John Gill was one of the first to stumble over the film crew. He said: "It's not every day I go out for a cycle ride and bump into Nikki and Jack from Silent Witness."
Neighbours have also watched as blue flashing lights lit up the darkness during dramatic night shoots along the seafront.
One quipped: "I haven't seen so many walkers on The Leas for years. Lots of people have been popping down to have a look to see what is going on."
Production manager Anne-Marie Kassar confirmed the 100-strong cast and crew were shooting scenes for the 26th series of the crime show.
She said: "I can't reveal the plot but the story is based on a fictional seaside town and Sheppey fits the bill perfectly. It has beautiful views and everyone has been so friendly and welcoming."
The new episodes are likely to be shown on BBC One early next year.