TOKYO —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% to 18,450.98 for its biggest single-day slide since Sept 29.

The Topix subindex for oil and coal shares added 0.8% 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% to end the day at 1,509.67 with all but two of its 33 subindexes in negative territory.

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