"After further analysis of specific balloon-shaped flying objects previously identified in Japanese airspace, including those in November 2019, June 2020 and September 2021, we have concluded that the balloons are strongly presumed to be unmanned reconnaissance balloons flown by China," the ministry said in a statement late Tuesday.

It said it had "strongly demanded China's government confirm the facts" of the incident and "that such a situation not occur again in the future".

"Violations of airspace by foreign unmanned reconnaissance balloons and other means are totally unacceptable," it added.

Beijing hit back on Wednesday, saying Japan lacked proof.

"Japan is making groundless accusations and smearing China without conclusive evidence. We are resolutely opposed to that," foreign ministry spokesman Wang Wenbin told reporters.

Japanese media said government officials were weighing relaxing rules on shooting down aerial objects that violate its airspace.

At the moment, weapons can only be used in case of a clear and present danger, Kyodo news agency reported.

"This case, I think, raises worries for us that may be a huge hole in Japan's defence," ruling-party security policy chief and former defence minister Itsunori Onodera told a meeting Wednesday.

Japan said last week it was re-analysing a series of incidents involving unidentified aerial objects in light of a Chinese spy balloon shot down by the United States after crossing US territory.

In the wake of the incident, the US military adjusted radar settings to detect smaller objects and discovered three more unidentified craft that President Joe Biden ordered shot down -- one over Alaska, another over Canada and the third over Lake Huron off Michigan.