Acting Sergeant Chris Thomson said police found a large number of unlocked vehicles in the Hamilton central business district last week, vulnerable to opportunistic thefts.

"During their patrol they have come across an unlocked vehicle with the keys still in the ignition," Acting Sergeant Thomson said.

"It's about people being vigilant, not leaving valuables in cars, ensuring vehicles are locked."

The discovery follows a spike in thefts from motor vehicles in the city last month.

"In December in the space four days there was at least nine, and they're on the rise again," Acting Sergeant Thomson said.

"In country towns the days are gone where you can leave your house and car unlocked.

"There are people who choose to do the wrong thing and unfortunately we don't live in a time we can be complacent about these things anymore."

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