Ai Weiwei has been under investigation for suspected economic crimes in accordance with the law late Wednesday, according to China's police authorities.

Ai has not been seen since Sunday, when he and an assistant said on Twitter that they had been taken into custody en route to Hong Kong, overseas media reported.

The detention of Ai was not reported by mainstream Chinese media, although there were a few discussions at online forums.

The New York Times said Ai's wife Lu Qing and several employees had also been taken into custody during a raid on his studio on the outskirts of Beijing on Sunday.

Police took away a computer, computer disks and other materials, Lu Qing was quoted as saying by AFP. She was not told the reason for the search or why Ai was taken away.

Ministry of Public Security publicity department chief Wen Guohui did not respond to a fax sent to him by the Global Times seeking to know the condition of Ai.

The incident should be addressed and resolved through correct legal procedures, Shi Yinhong, a professor with the School of International Studies at Renmin University of China in Beijing, told the Global Times Tuesday. In recent years, he said, the authorities have been more cautious and considered in handling detention cases.

"What Ai did may have crossed the bottom line of the law," Shi said. "And the government is just executing the function of maintaining stability."

The incident would not polarize Chinese society, Shi said.

He said it is improper to make a hasty conclusion about the relationship between Ai and the development of society.

"Such kinds of judgments should be made by historians in the future," Shi said.

Ai's studio in Shanghai was torn down in January by local authorities alleging Ai had failed to follow proper application procedures.