The number of China's AI companies ranked second in the global market, an expert said at the 2018 World Artificial Intelligence Conference in Shanghai on Monday.

"The number of China's AI companies continues to expand and now ranks second in the global market," said Liu Duo, head of China Academy of Information and Communications Technology.

Domestic patent applications have been increasing quickly since 2015, as industry and market investment have become more active and the scale of AI industry develops, especially in the audio and video fields.

Currently, domestic AI companies are developing quickest in Beijing, Shanghai, Guangdong, Zhejiang and Jiangsu, Liu added.

China has about 1,011 AI companies in the mainland, accounting for 20.53 percent of the world's total, following the United States with 2,028, according to a report by the China Institute of Science and Technology Policy at Tsinghua University.

The United Kingdom, Canada and India grabbed third to fifth spots on the list of countries with most AI companies, the 2018 China Artificial Intelligence Development Report said.

Beijing, with 395 AI companies, topped the list of cities with most AI companies worldwide, followed by San Francisco and London, with 287 and 274 companies respectively.

Shanghai, Shenzhen and Hangzhou also became part of the 20 world cities with the most AI companies.

AI companies were mainly established in China between 2012 and 2016. 2015 was the peak year, as 228 AI companies were founded then.

China's AI market scale reached 23.74 billion yuan ($3.46 billion) in 2017, up 67 percent year-on-year. Computer vision, with its core technologies such as image and video identification, had the largest market scale — 82.8 billion yuan last year, accounting for 34.9 percent of the total.