Chinese ambassador, Han Zhiqiang, has assured local authorities that Beijing supports the suppression of shady Chinese business in Thailand while also aiming to help boost bilateral trade and ties.
Mr Han made the remarks at a seminar on Tuesday marking the 49th anniversary of diplomatic ties between the two countries.
This came amid a furore over a Chinese-language billboard in the Huai Khwang area of Bangkok advertising a 30-day service for those wanting a foreign passport or citizenship that was spotted over the weekend.
According to Mr Han, more than 2,400 Chinese companies now operate in Thailand, of which about 1,400 have passed inspections by the Board of Investment (BoI).
Most are in the manufacturing and construction sectors, he said. They create benefits for Thailand through recruitment, investment and social and education projects, he said.
Chinese also run smaller firms in the service sector.
There are more than 700 Sichuan hotpot businesses in Bangkok.
However, some investments in this category may use grey capital for investment, Mr Han said.
"As for Chinese investors who invest in Thailand individually, some of whom are also connected to shady businesses, we admit that we see quite a few problems.
"They damage the benefits and put pressure on the competition of Thai SMEs. Some may also violate Thai laws. On this issue, the Thai and Chinese authorities should closely cooperate to enforce the law," he said.
Mr Han said China is willing to support Thailand in trade and investment, especially in agricultural products and tourism.
According to his report, total trade value between China and Thailand is US$120 billion, with China having a trade surplus of US$35 billion.
More than 85% of imported products from China are capital goods, which Thailand can further develop and export, such as silicone sheets.
Mr Han said that after Chinese companies set up solar cell sheet production companies in Thailand, they imported silicone sheets from China.
Last year, imports reached $1.2 billion. At the same time, Thailand has exported solar cell panels to foreign countries, especially Europe, worth $3 billion.
Mr Han said China welcomes Thai exports and is willing to help support Thailand in increasing exports to China, especially agricultural products, which account for 42% of the total.
Chinese tourists spent $10 billion here last year, he added.