China has granted preliminary approval for at least 35 trademarks linked to Donald Trump, documents on China's state trademark office show, giving the U.S. President and his family protection were they to develop the "Trump" brand in the market.

The trademarks, all variations in English and Chinese on the name "Donald Trump", were given preliminary approval in two lists published on the Trademark Office of the State Administration for Industry and Commerce on Feb. 27 and Monday.

The approvals underline the complexities and potential concerns over conflicts of interest facing President Trump, who has a sprawling business empire from hotels to apparel using the Trump name around the world.

Trump, a wealthy real estate developer, has previously said he has handed over his business interests to a trust overseen by one of his sons and a Trump Organization executive. He can, however, revoke the trust at will and, as its sole beneficiary, remains linked to it financially.

The new trademark approvals cover such businesses as branded spas, massage parlors, golf clubs, hotels, insurance, finance and real estate companies, retail shops, restaurants, bars and bodyguard and escort services.

The 35 trademarks, which Trump's lawyers applied for in April last year, are registered to "Donald J. Trump" and listed to the address of Trump Tower on Fifth Avenue in New York.

The Associated Press earlier reported the approvals of the trademarks, which it said also included three further trademarks not directly registered in the President's name. These related to Scion, a hotel brand Trump's sons want to expand in the United States. Reuters could not immediately confirm the three further approvals.

Representatives for the Trump Organization did not immediately respond to a request for comment.

Trump's personal ties between politics and business have prompted concern from politicians and rights groups who say the President could face potential conflicts of interest related to the extensive business affairs of his family.

Democratic Senator Ben Cardin, the ranking member on the U.S. Senate Foreign Relations Committee, called for the Departments of State, Commerce and Justice to brief Congress on the Chinese trademark approvals and on "the potential constitutional dangers that they present."

"This is an astonishing development ... It's clear to me that officials in Beijing have come to appreciate the potential return on investments for China in having a positive, personal business relationship with the President of the United States," Cardin said in a statement.

Cardin has previously introduced a resolution demanding Trump cut his ties with the Trump Organization or risk violating the Emoluments Clause of the Constitution, which bars public servants from accepting anything of value from foreign governments unless approved by Congress.

The preliminary approvals are open to be challenged for around a 90-day period from the date of approval. If no objections they will be formally registered in late May and early June respectively.

Trump received a single trademark approval last month in China for Trump-branded construction services, following a 10-year legal battle.