Commercial divers were hired to clear the metal from the area.

Flecker, a visiting fellow at the Institute of Southeast Asian Studies' archaeology unit, said that in 2015, while diving to retrieve the metal, project manager Ramdzan Salim and diver Ahmad Qamarulhazman found piles of ancient ceramic plates.

At about the same time, a 10-week-long archaeological dig was being carried out in Empress Place, Singapore.

Following media coverage of the findings, Salim and Qamarulhazman realized that some of the plates retrieved off Pedra Branca looked similar to artifacts discovered in Empress Place. They decided to hand the plates over to the institute for further research and safekeeping.

After the institute confirmed the plates were high-quality celadon ceramics from the 14th century, the National Heritage Board, or NHB, teamed up with the institute to conduct a survey at the Pedra Branca site, where a shipwreck was discovered in 2016.

After completing excavation work from the first wreck, the NHB and the institute conducted a survey off Pedra Branca, where they found a second shipwreck dating to the late 18th century. Efforts were made to excavate this wreck from 2019 to this year.

The first wreck was found about 100 meters northwest of the outcrop, the NHB and the institute announced on June 16, while the second was found 300 meters east of Pedra Branca.

Flecker said in an interview with The Straits Times that various Chinese ceramics formed the bulk of the haul from the first wreck, with some matching those previously unearthed in Singapore.

For example, Longquan greenware dishes from the first wreck match those unearthed earlier at Fort Canning, with both sets bearing a double-fish motif.

"From Fort Canning, there is a plate that is so similar you might almost be tempted to think they used the same stamp (to produce the motif)," Flecker said.

With research continuing, he said the find would be especially significant if it could be determined that the vessel was going to call at Singapore, which he believes it was.

More research will be carried out to improve knowledge of maritime trading in the region during the 14th century.