Prehistoric sites dating back 20,000 years were discovered in Vietnam's northern mountainous Lao Cai province, some 250 km northwest of capital Hanoi, said an archaeologist here on Thursday.

In areas covering about 20,000 square meters, hundreds of stone artifacts belonging to several prehistoric eras have been unearthed, Trinh Nang Chung from the Vietnam Institute of Archaeology was quoted by Vietnam's state-run news agency VNA as saying.

The oldest items are working tools made from pebbles found in rivers and springs, dating back 20,000 years.

There are also stone axes and disk-shaped tools belonging to the New Stone Age about 8,000-9,000 years ago. Four-millennium-old polished axes were also found, reported VNA.