NZ Police is urging caution after bad advice for walkers and trampers on social media.

There is a post circulating, particularly in outdoor, tramping and community groups on Facebook, recommending that people change their voicemail message rather than calling 111 when they are lost in the great outdoors and have low battery on their phone.

"This post contains incorrect advice that could be life threatening," a police spokesperson said.

"If you find yourself lost on a tramp or walk in the outdoors, and you have a weak signal or low battery, police advice is to call 111 immediately.

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"Do not waste time and phone battery trying to change your voicemail message.

"If you use up the last of your battery changing your voicemail, chances are nobody will know you need help.

"And if there is no cellular signal you will not even be able to change your voicemail message."

Police advise that before you go for a tramp or walk in the great outdoors, you let family and/or friends know where you’re going, and when to expect you back.

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"Even better – make use of the Plan my Walk app, which helps you plan and prepare your trip, including leaving trip intentions and advising contacts of your plans.

"And take a distress beacon! These can be hired for as little as $10 and are an absolute lifesaver if you are in a life-threatening situation and need help."

They can be hired or bought from outdoor stores and DOC visitor centres.