Researchers from the University of Hong Kong say they have made a significant discovery of fossils dating back millions of years to the Devonian, Permian and Jurassic periods.

They say the finds in Plover Cove, Sai Kung and Centre Island involve ammonite, trace and ostracod fossils and two of them are the largest of their type ever found in the territory.

Professor Chan Lung-sang from the university's department of earth science said it was after several expeditions that they managed to find the pieces of fossil.

He said the trace fossil contains worm burrows and evidence of previous life forms in mudflats.

"Fossils are mostly found in sedimentary rock and we do not have many exposures of sedimentary rocks around Hong Kong. So this time, we were able to find the ammonite piece, which indicates 190 million years ago in the Jurassic period the area around the current Hong Kong was like a sea area," Chan told RTHK.

"We were able to piece together the geological history and environment for that time period," he added.

Chan also said that more research will be conducted into the fossils and paleontologists may find something even more significant.

He said they plan to display some of the fossils discovered.