"That's the only way Apple can make an enormous impact on the environment," he said. The CEO said there has been enough talk about environment issues, and it's time to take action.

Cook's current visit is largely centered around environment. Aside from that, he will also be focusing on Apple Pay's entry in China.

"We very much want to get Apple Pay in China," he said. Apple has been negotiating with the banks and Jack Ma Yun from Alibaba, a China-based B2B platform provider, which would give a boost to a powerful third party payment provider. Alibaba was listed on NASDAQ last year.

Cook described the launch of Apple Pay in the United States as "a huge start" and believes that it could be even faster in China.

"I'm very bullish on Apple Pay in China," he said.

Apple Watch is another of his concerns. Cook said Apple Watch is a "perfect" product in one of the most popular categories right now. Apple is trying to make as many as it can. He did not, however, disclose the sales figures for the Apple Watch, which started on April 24.

IDC data showed that Apple has overtaken Xiaomi, a home rival, to become the No 1 smart phone vendor in China. He said he was excited about the "great news".

Apple announced on April 28 that it has sold 61 million iPhones in the first three months of this year. Cook said the company sold more iPhones in China than in the United States in last quarter.

He said the market potential of China is very large.

"I think China is a market where everyone will own a smart phone," he said, hoping to convince "a reasonable percentage" of the market.

Apple has accelerated market exploration in China, which Cook believes will become Apple's biggest market in the world. It has opened seven more retail stores in China since the start of 2015, aiming to bring the number of Apple Stores to 40 by 2016.

"Forty is a good objective for us for mid next year," said Cook, "That is not where we want to end. We'll keep adding from there."

Currently Apple has 22 retail stores in China since the first one opened its doors in Beijing in 2008.