Apple CEO Tim Cook was in China for the second time this year, he said on social media Tuesday, as the US technology giant seeks to shore up slumping sales in a crucial overseas market.

The iPhone maker remains popular among Chinese consumers but has ceded ground to domestic rivals in recent years as the Asian nation faces slowing economic growth and sluggish consumption.

Cook said Tuesday on his official account on social media platform Weibo that he had met with Chinese university students using Apple products to boost sustainable farming practices.

And in another video uploaded to his official page late Monday, Cook accompanied fashion photographer Chen Man on a walk through a historic quarter of the Chinese capital.

"It's great to be back in Beijing," Cook wrote.

Apple reported a $21.4 billion profit in the three months ending in June, on $85.8 billion in revenue over the period. The revenue was a five percent jump from a year ago.

But the iPhone maker's sales in China have come under pressure from homegrown competitors like Huawei in recent years.

The company was only the sixth-biggest smartphone vendor in China in the second quarter, down from the third biggest in the equivalent period last year, according to data by Canalys, a market analysis firm.

Cook last visited China in March, when he opened a new Apple store in Shanghai and attended a forum in Beijing alongside other top executives.