The Bank of Japan risks losing the confidence of investors by sticking to a bond-buying plan that is failing to drive inflation to its goal, says a former chief economist at the central bank.

"It wouldn't be sustainable" to buy government debt at a faster pace to spur consumer prices, Hideo Hayakawa said in an interview.

As bond purchases are the only way to boost base money at an annual pace of ¥80 trillion ($668 billion), the BOJ should scrap the policy. That would allow it to use other tools, including lowering the rate it pays on reserves, said Hayakawa, who spent most of his career under Gov. Haruhiko Kuroda's predecessors.