China's national rail freight volumes declined by a tenth in 2015, their biggest ever annual decline, business magazine Caixin reported, a figure likely to raise questions about how sharply the economy is really slowing. Citing sources from railway operator National Railway Administration, Caixin said rail freight volumes declined 10.5 percent year-on-year to 3.4 billion tons in 2015. Volumes fell only 4.7 percent in 2014. The amount of cargo moved by railways around China is seen as an indicator of domestic economic activity. The country's top economic planner said last month that November rail freight volumes fell 15.6 percent from a year earlier. Weighed by weak demand at home and abroad, factory overcapacity and cooling investment, China is expected to post its weakest economic growth in 25 years in 2015, with growth seen cooling to around 7 percent from 7.3 percent in 2014. But some China watchers believe real economic growth is already much weaker than official data suggests, pointing to falling freight volumes and weak electricity consumption among other measures. Power consumption in November inched up only 0.6 percent from a year earlier. A private-sector survey published on Monday showed that the factory activity contracted for the 10th straight month in December and at a sharper pace than in November, suggesting a continued gradual loss of momentum in the world's second-largest economy. A media official for the National Railway Administration said Caixin had obtained the figures from the railway operator's statistics department but said she was unable to confirm their accuracy as the 2015 report was not ready. Caixin said the operator was targeting an expansion in rail freight volumes to 4.2 billion tons by 2020, which would require an average annual growth rate of around 4.3 percent. In comparison, passenger traffic volumes on the network grew 6.1 percent in 2015, Caixin said, though at a slower pace from 2014 when it increased by 11.9 percent.