A majority of Japanese believe Prime Minister Shinzo Abe bears some responsibility for altered documents at the centre of suspicions of a cover-up linked to cronyism, according to an opinion poll yesterday that also showed his support sliding.

In his worst crisis since taking office in 2012, Abe and Finance Minister Taro Aso have been under fire since the finance ministry said on March 12 it had altered records relating to a discounted sale of state-owned land to school operator Moritomo Gakuen, which had ties to Abe's wife, Akie.

References to Abe, his wife, and Aso were removed from the finance ministry's records of the sale, copies of documents released by the ministry showed.

Both men have denied any wrongdoing in the affair.

But 66.1 percent of respondents to a poll conducted by Kyodo news agency on Saturday and yesterday said they felt the premier had some responsibility for the altered documents. Only 25.8 percent said they thought he didn't.

Protesters have flocked to the streets by the prime minister's office every night since the ministry admitted altering the documents, with some 2,000 on Friday calling for Abe and Aso to resign.