TOKYO, Jan 4 (Reuters) - Japan's Nikkei share average tumbled to a 2-1/2 month low on Monday after weak China factory activity surveys and year-end losses on Wall Street discouraged investors on the first trading day of 2016.
The benchmark Nikkei average fell 3.1 percent to 18,450.98 for its biggest single-day slide since Sept. 29.
The Topix subindex for oil and coal shares added 0.8 percent to buck the day's weakness as oil prices surged amid tensions between top crude producers Saudi Arabia and Iran.
The broader Topix shed 2.4 percent to end the day at 1,509.67 with all but two of its 33 subindexes in negative territory.
The JPX-Nikkei Index 400 fell 2.5 percent to 13,597.24. (Reporting by Joshua Hunt and Ayai Tomisawa)