A California transit employee killed eight co-workers and wounded another before taking his own life on Wednesday in the latest of a spate of deadly mass US shootings, prompting the state's governor to ask: "What the hell is wrong with us?"

Authorities did not immediately offer many details or a possible motive for the shooting, which unfolded about 6.30am Pacific Time (9pm last night in Malaysia) at a light rail yard for commuter trains of the Santa Clara Valley Transportation Authority (VTA)...