(ShareCast News) - Japanese car maker Toyota posted a record first quarter profit, as a weakening yen offset sluggish demand in Japan and Southeast Asia.In the three months to end of June, the group posted a 10% year-on-year profit to 646.39bn yen (£3.35bn), ahead of analysts' expectations of a 607.5bn yen figure.Operating profit rose 9.1% to 756bn yen, while revenue was 9.3% higher than in the corresponding period a year ago.Sales growth remained sedate as the car maker maintained a self-imposed cap on production capacity in a bid to prevent quality problems, having only lifted the three-year freeze in April for its plants in Mexico and China.In China, the world's biggest car market, sales suffered from intensifying price competition and declined 0.1% compared to the previous three months, which contributed to a 0.4% slip in global sales to 2.502m vehicles."Our April-June [China] sales volume growth was strong, but we can't be optimistic when it comes to profits," Tetsuya Otake, Toyota's managing officer, said at a news conference in Tokyo.Despite the decline sales in China, the group has outperformed some of its main rivals, with sales growing 10% year-on-year, compared with a 4.4% increase for General Motors and a 3.9% drop reported by Volkswagen.In a separate statement on Tuesday, the Japanese automaker confirmed it would invest 59bn yen to build a new line at its Tianjin plant in China, which is expected to become operational by mid-2018.New York-listed Toyota shares were down 3.45% to $128.58 at 1616 BST on Tuesday.