(Adds details, background on China, its key market) Feb 20...

(Adds details, background on China, its key market)

Feb 20 (Reuters) - New Zealand's a2 Milk Company Ltd (ATM) reported on Wednesday a more than 50 percent jump in half-year net profit, as the company expanded market share in China despite slowing demand there.

The dairy producer has weathered a slowdown in consumer spending in its largest market, China, which has seen domestic demand falter amid a trade dispute with the United States.

Net profit was NZ$152.7 million ($105.07 million) for the six months to Dec. 31, the first half of the company's financial year, compared with NZ$98.5 million in the same period a year earlier, the company said in a statement.

The company lifted its market share in China by pushing into smaller cities. It said it would reinvest the benefits of scale into increased marketing activities in the second half.

Chinese parents have embraced the company's infant milk powder that is marketed as easier to digest than conventional milk because it lacks the A1 caesin protein.

But competition has increased as others such as Nestle SA NESN.S launch A1-free infant formulas in China.

The company said total revenue for the half year jumped 41 percent to NZ$613.1 million, while revenue from China and other Asia markets grew about 50 percent.

Revenue growth in the second half is expected to be broadly in line with the first half, the company said in a statement.

The company's shares gained 38 percent in 2018, outperforming a 4.9 percent rise in the benchmark S&P/NZX 50 index (nz50) .

In a separate release, New Zealand dairy giant Fonterra (FSF) (FCG) said it was signing up farms to supply milk for a2 in the 2019/2020 season.

However, Australian vitamin maker Blackmores Ltd (BKL) said weak sales in China, its biggest export market, would weigh on its net profit in the second half of the year, driving down its shares the most since the company listed three decades ago.

($1 = 1.4533 New Zealand dollars)