Mainland automakers roared forward on Monday as shares of Guangzhou Automobile Group jumped the most in a month after the company reported that total vehicle sales in May surged by more than 20%.

Investors cheered Guangzhou Automobile’s announcement after market close on Friday that vehicle sales in May increased to 165,505 from 135,389 in the same period last year. The automaker has sold 792,457 vehicles so far this year. It climbed by 4.7% on Monday to HK$13.32, with more than HK$500 million (US$64.1 million) worth of shares changing hands.

Meanwhile, Geely Automobile Holdings continued its winning streak, rising for the tenth time in 11 trading sessions. It edged up 1.6% to HK$14.40 and is the best performer on Hong Kong’s benchmark Hang Seng Index this year, gaining 94.3% so far. The recent rally in the Hangzhou-based automaker gained momentum after Zhejiang Geely Holding, which indirectly controls about 44% of Geely Automobile, announced on May 24 it had reached an agreement to purchase a 49.9% stake in Malaysia automaker Proton Holdings and a 51% interest in its British subsidiary Lotus Cars.

Elsewhere, Great Wall Motor Company increased 2.1% to HK$8.73 and Dongfeng Motor Group gained 1.9% to HK$9.05.

Mainland auto stocks have been a hot ticket for investors this year amid the boom in China’s car production. The government is aiming for sales of 35 million vehicles in 2025, up from 28 million last year. That target hit a speed bump after data last month showed passenger vehicle sales in April dropped 3.7% from the same period last year, but total vehicle sales are still up 4.6% year-on-year in the first four months of 2017.

While mainland automakers have surged forward this year, Japan’s leading car producers have been stuck in a tailspin. Toyota Motor Co., Subaru Corp. and Mazda Motor Corp. have all reported drops in operating profit exceeding 25% for the previous fiscal year.

A slump in the US dollar has weighed on Japan’s automakers as proceeds from overseas sales are diminished when repatriated back to Japan. The greenback traded near to a six-week low against the yen on Monday at 110.49.

Among 2,013 members on Japan’s TOPIX, Mazda is the 38th worst-performer so far this year, down 20.7% to 1,517 yen (US$13.73). Subaru is the 40th worst performer and Toyota ranks as the 105th worst, according to Bloomberg data.