China's most-wanted fugitive returned from the US Wednesday and surrendered, authorities in Beijing said, despite the two countries lacking an extradition treaty.

Yang Xiuzhu, 70, was number one on a list of China's top 100 fugitives that it circulated through Interpol last year as it promoted its "Sky Net" effort to repatriate corrupt officials.

The drive is part of the high-profile anti-graft campaign launched under President Xi Jinping, who has said that the scourge threatens the Communist Party's grip on power.

But it is hampered by the fact that most Western countries, including the US, do not have extradition agreements with China, where courts are overseen by the ruling party and the use of force by law enforcers to extract confessions is believed to be common.

Yang was the 37th fugitive to be repatriated thus far, according to the Communist Party's internal watchdog the Central Commission for Discipline Inspection (CCDI), but the exact circumstances of many of the returns are not clear.

Formerly deputy director of the construction bureau of eastern Zhejiang province, she was wanted by authorities for embezzling more than $40 million.

Yang landed in Beijing after living overseas for 13 years eluding authorities, the CCDI said in a statement.

She fled in 2003, first to Hong Kong, Singapore, France, the Netherlands, and Italy, before going to the US in 2014, where she sought asylum the following year.

Anti-corruption investigators brought pressure on Yang through diplomatic, judicial, law-enforcement, and other channels, the CCDI said, urging her to stop resisting and surrender in order to obtain lighter punishment.

The death penalty is available for some corruption cases in China, which overseas rights groups say is the world's biggest executioner.

"Yang Xiuzhu decided to turn herself in from initially saying 'if I'm going to die I'll die in the US," to 'thinking of coming home', and at last her withdrawing her asylum application," it said.

Her repatriation was an "important achievement" of China-US law enforcement cooperation, it added.

China thanked the US for its assistance, foreign ministry spokesman Geng Shuang said at a normal press briefing Wednesday.

Her repatriation came days before the countries hold a law enforcement summit in Beijing.

Yang's younger brother was repatriated from the US in 2015 on corruption charges, which the CCDI said dealt her a psychological shock.

In 2015 she was detained by US Immigration and Customs Enforcement for violating visa rules. She withdrew her asylum application in July and the next month immigration authorities approved her repatriation, the CCDI said.

Yang's return shows that "America is not the fantasy of a 'fugitives' paradise'," the CCDI said.