The entire second floor of a Caroline Springs house was used to grow 320 cannabis plants, police say.

Police were called to a double-storey property on The Esplanade about 5am last Monday week after 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.

The trio had fled by the time police arrived, but they did leave a car behind.

Early estimations of 220 plants growing at the property were far short of the final haul.

“There’s roughly 120 seedlings, small seedlings, and about another 100 medium to large cannabis plants,” Senior Constable Symons estimated at first.

“It’s quite large,” he said.

“They were all growing in the upstairs area. The house was very sparsely furnished, just the one bed.”

Senior Constable Symons was told by neighbours they’d noticed people coming and going from the property at different times of the day and night.

No arrests have been made.

In January, a police raid at a Derrimut warehouse uncovered 731 cannabis plants with a street value in the “hundreds of thousands of dollars”.

Cannabis offences in Brimbank have more than doubled over the past decade, latest Crime Statistics Agency figures show.

Offences jump from 131 cases in 2006 to 308 in 2016, in the year to March 31.