The lawyer for Chinese artist Ai Weiwei said Monday the tax office in Beijing has refused to accept money the activist needs to pay in order to lodge an appeal against a huge tax bill.

Pu Zhiqiang told AFP that officials had "changed their mind" and would not accept the eight million yuan ($1.3 million) needed to be paid in order for Ai to pursue an "administrative revision" of the 15 million yuan bill.

The deadline for the tax payment is Tuesday.

"They now refuse to accept the guarantee payment so I need to discuss this matter with Ai Weiwei," Pu said as he drove to the artist's studio in the Chinese capital.

An official at the Beijing tax office declined to comment when contacted by AFP.

Ai disappeared into police custody for 81 days earlier this year and was ordered to pay the back taxes after his release.

But the artist, best known for his role in designing Beijing's "Bird's Nest" Olympic stadium, said last week he will contest the order and will use funds donated by supporters as a guarantee to make an appeal -- a step required by Chinese law.

Ai has denied any wrongdoing and insists the government is trying to silence him and his vocal human rights activism.

The drive to donate to Ai has gathered momentum since beginning more than a week ago, with supporters coming from as far afield as Hainan island in the south, 3,000 kilometres (1,860 miles) away, to give money.

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, including banknotes folded into paper planes.

Total donations had reached 6.7 million yuan, Liu Yanping, who works with Ai, said on her Twitter account last Thursday.