(Refiles to fix format)
* Q3 annualised GDP seen +1.3 pct vs +2.5 pct in Q2 2017
* External demand helped economic growth
* GDP due at 2350 GMT Nov 14
TOKYO, Nov 10 (Reuters) - Japan's economy was expected have grown for a seventh straight quarter in July-September, a period of unbroken expansion last seen between 1999 and 2001, a Reuters poll found on Friday.
Gross domestic product (GDP) is expected to have grown at an annualised rate of 1.3 percent in the third quarter, the poll of 20 analysts showed.
That result would mark a seventh straight growth quarter, the longest period of expansion since an eight-quarter run from April-June 1999 to January-March 2001.
Quarter-on-quarter growth of 0.3 percent is expected after a revised 0.6 percent rise in the second quarter.
"Consumer spending was seen stalling in July-September but export growth likely supported solid economic expansion," said Atsushi Takeda, chief economist at Itochu Economic Research Institute.
The poll found that private consumption, which accounts for roughly 60 percent of GDP, probably slipped 0.4 percent in the third quarter, the first fall in seven quarters.
External demand - or exports minus imports - was seen contributing 0.4 percentage point to growth, the poll found, after it subtracted 0.3 percentage point from GDP growth in April-June.
Capital spending was seen rising 0.3 percent in the third quarter, growing for a fourth straight quarter, following a 0.5 percent rise the previous quarter.
"We forecast the economy will continue to grow as both domestic and external demand pick up thanks to the global economic recovery and a softer yen," said Hidenobu Tokuda, senior economist at Mizuho Research Institute.
"But there is downside risk from the Chinese economy and we also need to closely monitor geopolitical risk from the North Korean situation," he said.
The Cabinet Office will announce the GDP data on Nov. 15 at 8:50 a.m.(2350 GMT, Nov. 14).
The Bank of Japan's corporate goods price index (CGPI), which measures the prices companies charge each other for goods and services, was seen likely to have risen an annual 3.1 percent in October, the poll found.
Such a result would mark a 10th straight rising month and the fastest annual rate of increase since October 2008, excluding the effect of a sales tax hike in 2014.
The central bank will release the CGPI data on Nov 14 at 2350 gmt. (Reporting by Kaori Kaneko; Editing by Eric Meijer)