Law enforcement sources tell TMZ, Bella's house was hit by thieves only days after an earlier attempted break-in, and police are now investigating.

Sources say burglars made off with around $150k in valuables ... and they used her designer luggage to transport the stolen goods out of the house!!!

We're told the intruders smashed the front window and entered the home shortly after Bella left. They were caught on surveillance, but covered their faces with bandanas. The footage was passed on to police.

Sources say Bella's designer jewelry, vintage clothing and purses are all missing ... as are the Chanel and Louis Vuitton luggage used to haul off the loot.

It's the second time this month Bella's San Fernando Valley home has been targeted by burglars.

As we reported ... Bella had a huge scare last month when someone broke a window and tried to enter the pad. She was home at the time, and the would-be thieves ran away ... but someone eventually hit the jackpot.

And Bella's not the only one this week to be hit twice by burglars. Christina Milian's home was burglarized twice while she was out of the country.