Thieves stole donation gifted to boost the funds of the Great North Air Ambulance as well as property belonging to the charity's staff.
The break-in happened at the North East-wide charity's headquarters, when burglars forced their way through a fire door and carried a search of the property.
They found and then made off with diamond rings which had been donated to the charity by members of the public, and a significant amount of store cards donated by local supermarkets and other organisations.
Also stolen were car keys, charity cash collections and personal items belonging to members of staff.
A significant amount of damage was also caused to the office during the burglary.
Mandy Drake, head of fundraising at GNAAS, said: “We are all shaken by this.
"We just don’t understand why someone would steal from a charity, where every penny makes a difference.
“Amongst the items stolen were prizes to support our fundraising efforts at our ball on June 4 in Newcastle.
"The money raised at this event goes toward the ongoing work of our aircraft and crew.
"If anyone is able to help plug this gap by donating more prizes, we would be forever grateful.
“Measures have been taken to prevent further such incidents, and we would like to reassure our supporters that their donations are safe in our hands.”
The break-in happened at the charity's office in the Imperial Centre in Grange Road, Darlington, sometime between 5.45pm and 9pm on the evening of Thursday, March 10.
If anyone has any information about the break-in they are asked to ring police on 101 and ask for Detective Constable Neil Stannard of Darlington CID.