World War I medals stolen from a veteran's grandson have been anonymously returned to a war memorial museum.

On Wednesday, Patrick Conlon called police after a parcel containing the medals was allegedly stolen from his mailbox in Wellsford, Auckland.

Police said Conlon was very upset by the theft of the medals as they were awarded to his late grandfather, Elmer James Conlon.

Police appealed to the public for any information that could help locate the medals.

On Saturday, police were contacted by the Wellsford War Memorial Museum staff advising that the medals had been found in their returns bin.

Senior Sergeant Damian Lawn said it appears someone had dropped them off overnight.

"We're pleased that whoever took these medals did the right thing and returned them - obviously they are hugely significant to Mr Conlon and we are glad to be able to reunite him with them," Lawn said.

"We have fingerprinted the medals before returning them and we are continuing with our enquiries."

Anyone who has any further information about the theft or those involved is asked to get in touch through our 105 service, using reference number 250709/8286.