The new US ambassador to China Max Baucus chided Beijing on Wednesday for a wave of arrests of "moderate voices", in his first public address since arriving in March.

Baucus, who succeeded Gary Locke, did not name names in his speech to businesspeople but told them that greater rights protections would strengthen US-China relations.

Activists and others in China have come under increasing pressure from ruling Communist Party authorities.

"In the past year, China has arrested several moderate voices who had peacefully advocated for such basic things as good governance, the rights of ethnic minorities and the rule of law," Baucus said at a lunch hosted by groups including the American Chamber of Commerce in China.

"We strongly believe that individual advocates play an important role in developing civil society," he added.

"Protecting basic rights such as freedom of expression enhances social stability and human dignity and will strengthen the foundation upon which our bilateral relationship is built."

President Xi Jinping has moved to crack down on dissent since taking office last year, with authorities suppressing online dissent and detaining activists considered even moderate critics of Beijing.

Pu Zhiqiang, one of the country's most celebrated rights lawyers, was arrested earlier this month on suspicion of "creating disturbances and illegally obtaining personal information".

That followed January's sentencing of prominent legal activist Xu Zhiyong to four years in prison for backing demonstrations calling on officials to disclose their assets.

Uighur academic Ilham Tohti, a critic of government policy towards the ethnic minority, was detained the same month and has been charged with separatism, which can carry the death penalty.

Washington and Beijing have disagreements in several areas, including the recent US indictment of five Chinese military officers for alleged cyber-espionage.

Such behaviour was "criminal in nature", Baucus said.

As a US senator Baucus played a key role in paving the way for China's entry into the World Trade Organisation and he called for greater US-China cooperation, particularly on economic issues.

He urged progress on a US-China bilateral investment treaty, which he said "could do for China's investment regime what WTO accession did 15 years ago".

Baucus dismissed the notion that Washington was seeking to contain China in Asia as "simply untrue", maintaining that "the United States welcomes China's rise".