Sadly for Kate Hudson, the men dressed in police uniforms who arrived at her pre-Halloween party around 1 a.m. Sunday morning were real LAPD officers.

The cops came to Hudson's Brentwood home to move her party indoors and keep the noise down for the neighbors.

A source told us that the single mom "was dressed as a '60s flight attendant" and her son, Ryder Robinson, "was nowhere in sight."

Among the guests: Courteney Cox went dressed as a witch with husband David Arquette as a warlock, Winona Ryder was a mouse, Rachel Zoe donned a flapper costume, and Cindy Crawford dolled up as Amy Winehouse.

But cowboy-clad Gerard Butler was the main attraction. Our insider reports, "All the girls at the party were lining up to talk to Gerard . . . he left with two very sexy vampires."

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