The entire top floor of a Caroline Springs house was being used to grow 321 cannabis plants, police say.

Police were called to a double storey property on The Esplanade around 5am this morning following reports of three people attempting a “targeted” break in.

Melton Police Detective Senior Constable Shannon Symons said the would-be thieves broke down the front door.

“They were inside the house when they (a neighbour) called the police,” he said.

“They (the thieves) had their faces covered.

“There’s roughly 120 seedlings, small seedlings, and approximately another 100 medium to large cannabis plants.

“They were all growing in the upstairs area.

“The house was very sparsely furnished, just the one bed.”

He said the bust was on par with many in the area of recent times.

“It’s quite large,” he said.

Snr Con Symons said residents in the street had noticed people come and go from the property at various times of the day and night.

The trio left a car behind, police say.

No arrests have yet been made.