The theft took place at about 14:15 BST at the Amber Shop and Museum in Market Place.
A Suffolk Police spokesman said the theft was carried out by a man and woman. No violence was used and it is believed they stole items from a display in the shop.
They then ran off down an alleyway., Anyone with any information is asked to call Suffolk Police.
Jewellery worth about £10,000 has been stolen during a raid in Southwold.