The actress, 33, is set to exchange vows with music producer Benny Blanco, 37, at a vast clifftop plantation called Hope Ranch estate in Goleta, overlooking the Pacific Ocean, this weekend, with contractors seen preparing marquees on Friday.
Her rehearsal dinner took place on Friday night at a 10-bedroom mansion built in the 1930s, owned by insurance executive Greg Econn.
Guests including Selena's Only Murders in the Building co-stars Martin Short and Steve Martin, as well as Paul Rudd, were chauffeured to the property in a fleet of Mercedes buses.
Swift, who is staying at the Rosewood Miramar resort in Montecito, was brought separately in a motorcade.
Photos published by the Daily Mail showed the sprawling property decorated with tubs of flowers and strings of fairy lights ahead of the main ceremony, which will take place at Sea Crest Nursery in Goleta.
Security has been intensified, with reports Gomez is spending around $US300,000 ($A458,716) to safeguard the weekend.
A source quoted by the Daily Mail said Swift had flown in from Kansas City earlier in the day on Friday, travelling without her fiancé, American football star Travis Kelce, 35, who is preparing for the Kansas City Chiefs' game against the Baltimore Ravens.
Swift, who once promised Gomez she would be her flower girl, has been a longtime friend of the singer and will be among the 170 guests at the nuptials.
Most of the wedding party are staying at El Encanto, a Santa Barbara resort owned by Tinder co-founder Justin Mateen, where rooms start at $US1,000 ($A1,529) per night.
Other attendees include Paris Hilton.
Before heading to the rehearsal dinner, Martin, Short and Rudd were seen socialising at El Encanto.
Martin co-created Only Murders in the Building, which has run for five seasons and features Gomez, Short and Martin in lead roles, with Rudd guest-starring in recent seasons.
Gomez and Blanco confirmed their engagement in December with an Instagram post captioned: "Forever begins now."
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