Thousands of people have donated 5.29 million yuan ($830,000) to help Ai Weiwei pay a huge tax fine, with some throwing money wrapped in paper planes into his garden, the Chinese artist said on Monday.

The drive to donate to Ai, who disappeared into secret police custody for 81 days this year and has since been ordered to pay a 15 million yuan tax bill, began on Friday and has gathered momentum mainly from the Internet.

"The postal bureau has just notified me that there are 776 cash remittances that we need to go and pick up," Ai - also a vocal rights activist - said on Monday morning, adding more than four million yuan had already been donated.

By early afternoon, that sum had risen to 5.29 million yuan with 18,829 people contributing towards the bill, Liu Yanping - who works with Ai - said.

But the state-run Global Times newspaper suggested on Monday in an editorial that experts could charge Ai with 'illegal fundraising' for accepting contributions for the crippling tax bill he has to pay by November 15.

The 54-year-old, who had a prominent exhibition at London's Tate Modern earlier this year, has denied any wrongdoing and insists authorities are trying to silence his rights activism by accusing him of tax evasion.

His mother has offered to sell the house left to the family by Ai's father, the late Ai Qing, a well-known poet praised by the Communist Party but who also suffered political persecution.

Supporters have been sending Ai money through Internet and bank transfers, while some have even resorted to throwing cash over the walls into his courtyard home, he said.

"Every morning we have to pick up the money thrown into the courtyard. Sometimes they are folding it into planes or boats," he said.

Ai was detained in April to a global outcry, at the same time as scores of activists were rounded up amid anonymous calls on the Internet for street protests in China similar to those that toppled governments in the Arab world.

He had earlier incensed the government by organising independent investigations into the collapse of school houses in the 2008 Sichuan earthquake and into a 2010 fire at a Shanghai high-rise that killed dozens.

He says police beat him when he tried to testify on behalf of another activist in 2009.

On Twitter, Liu posted details for supporters keen to donate money through the postal service, bank or via the Internet.

But Ai, whose art works have sold worldwide - some reportedly for hundreds of thousands of dollars - said that he does not need the financial support.

"What I need is the ethical support of everybody. I don't need the money," he said. He has vowed to pay back the money to his donours, some of whom are prominent activists.

Ai Xiaoming, a professor at Zhongshan University in south China's Guangdong province and a democracy campaigner, said last week she had helped raise 400,000 yuan for the artist.

Hu Jia, another famous rights activist who was released from prison earlier this year, said in a Twitter posting he donated 1,000 yuan to Ai for 'my great gratitude and respect for what he has done'.

Last month Ai was named the world's most powerful art figure by influential British magazine Art Review.