* Nikkei up 0.02%, Topix adds 0.37%
* Weak yen helps, but US-China woes, Brexit concerns limit rise
By Shinichi Saoshiro
TOKYO, Sept 3 (Reuters) - Japanese shares eked out gains on Tuesday as a weaker yen propped up exporting firms, although negative factors including the U.S.-China trade war and Brexit concerns curbed market sentiment.
The Nikkei share average ended the day up 0.02% at 20,625.16, bucking a more bearish trend in Asia.
There were 146 advancers on the Nikkei index against 71 decliners.
The index seems to have found some support having probed multi-month lows several times over the past month.
"The Nikkei looks surprisingly steady, with the 20,500 level for the index proving to be a threshold that attracts bargain hunters," said Jun Kitazawa, deputy manager of investment information at Miki Securities.
Still, the Nikkei's gains were modest without leads from the U.S. markets, which were closed on Monday for holiday.
Also adding to investor caution was the prospect of more Brexit-related market turmoil.
British lawmakers decide later on Tuesday whether to move Britain a step closer to an early election, when they vote on the first stage of their plan to block Prime Minister Boris Johnson from pursuing a no-deal Brexit.
Shares of major exporters advanced as the yen edged further away from an eight-month high marked against the dollar last week.
Toyota Motor Corp climbed 0.8%, Subaru was up 2.4% and Panasonic added 0.6%.
Nickel-related companies gained as the price of the metal soared to a five-year high on supply concerns with top producer Indonesia announcing curbs on ore exports from January 2020, two years earlier than initially flagged.
Sumitomo Metal Mining Co climbed 1.8% and Pacific Metals Co gained 2.7%.
Residential and office property firms advanced as a recent drop in long-term bond yields nudged investor money towards real estate offering higher returns.
Cosmos Initia Co surged 7.5%, Tosei Corp added 3.3% and Pressance Corp gained 1.8%.
The broader Topix gained 0.37% to 1,510.79.
The stocks that gained the most among the top 30 core Topix names were Hitachi, which rose 1.8%, followed by Shin-Etsu Chemical Co's 1.6% gain.
The worst performers among the Topix 30 were Fanuc Corp , which lost 2.3%, followed by Keyence Corp, down 1.1%.
Share volumes on the Tokyo Stock Exchange's main board were 0.84 billion, compared with the average of 1.1 billion yen in the past 30 days. (Additional reporting by the Tokyo markets team; Editing by Sam Holmes)