Consumer New Zealand adviser Maggie Edwards said airlines would only accept limited liability if they were at fault- for example if checked baggage or items like prams that customers were forced to hand over was lost or damaged.
Airline staff fulfilled their obligations by screening potential employees, but if an airline worker was found to be culpable for a theft, the airline might agree to pay, Edwards said.
However in the case where a valuable was kept in checked baggage that wasn't being kept an eye on, the airline wouldn't be liable under its conditions of carriage.
Air New Zealand specifically issued warnings to passengers about not putting valuables in their hand luggage, she said.
"Things do go missing on flights," she said.
"It's a bit like being on a train. Even though you're being cooped up there's always someone to see an opportunity (to steal). (Airline staff) aren't babysitting your luggage in the overhead lockers, it's best to keep it on you."
Jetstar spokesman Phil Boeyen said onboard thefts were "extremely rare" and as customers looked after their own cabin baggage, the airline wasn't liable for theft.
"If the allegation was serious our crew would assess the information and use their discretion around alerting authorities prior to arrival."
Allianz New Zealand chief sales officer Will Ashcroft said it was unlikely an airline would agree to take responsibility for items stolen on a flight.
"From a travel insurance perspective, travellers should not expect to be covered for items that are left unattended in a public place."
Not all scenarios were the same, he said, and given the rarity of onboard thefts, each case would be assessed individually.
"Travellers that go to the bathroom mid-flight, leaving their wallet, phone, passport and valuables on show, would not be covered should these items get stolen," he said.
"However, items that are stolen from bags in overhead lockers are likely to be looked at more favourably by travel insurance companies, as you can't be expected to keep an eye on all your possessions for the entire flight, especially on long haul journeys."
Southern Cross said it would insure travellers on losses such as a midair theft on a case by case basis, and would assess if "reasonable care" was taken to secure the belongings.
The degree of care needed was proportional to the value of the items, a spokesperson said.
"For example, we wouldn't consider leaving an expensive necklace unattended in plain view on your seat while you went to the toilet to be taking reasonable care. But if you had the necklace stowed away in your cabin baggage out of sight, then we would consider this to be reasonable care."
