They say two masked men smashed glass displays after overpowering a guard.
Local mayor Thymios Kotzias said items of "incalculable" value had been stolen, but gave no details.
Culture Minister Pavlos Geroulanos has tendered his resignation, but it has so far not been accepted. He is on his way to the site in western Greece.
The armed thieves are reported to have entered the museum at 07:30 on Friday (05:30 GMT) and demanded that a female employee hand over various objects.
.......itu sebagian kutipan BBC News......kalau kompas menurunkan berita dengan Judul : " Maling Berkerudung Curi Koleksi Museum Olympia "....
pertanyaan saya : apakah Masked men = Maling berkerudung ??..........
