A dozen rare colonial coins worth almost $1 million are stolen from the State Library of NSW.

Police said a man smashed a glass display cabinet and stole the 12 coins about 3:40pm (AEST) on Wednesday.

The coins, contained in a secure display case, were from the period between the 1850s and the 1920s.

The included a "Holey Dollar" from the early 19th century, so named because of the hole punched in the centre of the coin.

They also included a "Dump", a coin created from the centre of the Holey Dollar after it had been removed.

State librarian Alex Byrne said the 12 coins were among 15 on display at the library.

"We are deeply disappointed by this callous act of public vandalism," Dr Byrne said.

Police said the same thief could be responsible for stealing jewellery from a CBD a hotel less than two hours later.

At 5:20pm, a man entered the George Street building, approached a glass cabinet and took four sets of diamond earrings, three diamond rings and a gold pendant.

The jewellery is worth an estimated $75,000.

Forensic specialists were working to determine whether the thefts were linked.

Stolen coins linked to colonial history

A "Dump" coin stolen from the NSW State Library dates back to the early 1800s. ( Supplied: NSW State Library )

Holey Dollar coins were created by stamping a hole in imported Spanish coins that arrived in Australia in the 1800s.

"In the early 19th century, there was a shortage of coins in the colony of New South Wales," the library's display material said.

"Governor [Lachlan] Macquarie's solution to the problem involved recycling Spanish currency to create the first uniquely Australian coinage.

"Macquarie directed William Henshall, a convicted forger, to cut out the circular centre piece from each of the 40,000 Spanish dollars that arrived in the colony in 1812.

"[Governor Macquarie] set their value at five shillings for the Holey Dollar and 15 pence for the Dump."