Britney Spears and Sam Asghari's Wedding Preparations Underway with Massive Tent

Britney Spears' big day is finally here -- and wedding prep continues -- with a massive tent popping up, where she'll say her "I do's" to fiancé Sam Asghari.

Check out the photos ... you can see crews hard at work outside the L.A. location while they put some of the finishing touches in place. The white tent appears to be there for max privacy, with a staircase leading to the entrance. You can imagine there are plenty of flowers, tables and chairs being packed inside as well.

TMZ broke the story -- Britney and Sam will get married Thursday in an intimate ceremony of about 100 close friends and family members. We're told Britney's brother, Bryan, will be there ... but her sister, Jamie Lynn, and her parents were not invited.

It's also still not clear who will give Britney away at the altar -- or if they'll even have a traditional ceremony.