(Adds comment, details)
* Oct copper imports at 406,708 tonnes, off 18-month high in Sept
* Arrivals still the third-largest this year
HONG KONG, Nov 8 (Reuters) - China's copper arrivals fell 11.2 percent in October, coming off an 18-month high in the previous month due to poor price differentials between domestic and international copper markets and as a week-long holiday cut shipments.
Arrivals of anode, refined metal, alloy and semi-finished copper products hit 406,708 tonnes in October, down from 457,847 tonnes in September, Chinese customs data showed on Friday.
Analysts and traders in China had expected fewer arrivals of copper in October given that the long national holiday had cut working days on customs checks.
The arrivals were up 26.4 percent from a year ago, according to Reuters' calculations based on customs data for October 2012.
Benchmark three-month London Metal Exchange copper price rose slightly to $7,158.25 per tonne after the release of Chinese data.
"The key reason for lower arrivals of copper in October was that price differentials were not good in the month, discouraging spot purchases by importers," said Zhou Jie, a trading manager at China International Futures (Shanghai).
He added that the week-long holiday at the start of the month also had slowed arrivals.
The October imports were still the third-highest this year due to steady consumption in the world's top consumer of copper.
Importers have been keen to use copper as collateral for short-term loans, expecting a cash crunch in the domestic market ahead of the year-end, according to the traders.
Traders said increased interests by importers had cut the availability of copper in bonded warehouses in Shanghai, pushing buyers to get shipments from the international market.
Bonded stocks in Shanghai have stayed at a 1-1/2-year low of around 400,000 tonnes over the past month, traders estimated, compared with a record of about one million tonnes in the first quarter. The bulk of the stocks were not offered on the market.
Spot standard grades of refined copper in bonded warehouses in Shanghai or metal due to arrive soon traded at premiums of $190-$200 a tonne this week, compared with $175-$200 at the end of September, traders said.
Some end-users received more orders in November, driving up their purchases of spot copper.
"Our orders in November rose 10 percent from October. November usually is not a peak consumption season for our products," said a trader at a producer of copper tubes.
Copper imports dropped 7 percent to 3.67 million tonnes in the first 10 months of 2013, compared with the same period last year, the data showed.
(Reporting by Polly Yam; Editing by Richard Pullin and Tom Hogue)