China and Japan accused each other on Saturday of violating their territorial airspace over disputed islets, with Tokyo formalising its protest by summoning the Chinese envoy and asking that such an incident not occur again.

However, Beijing claimed that a Japanese civilian aircraft "illegally entered China's airspace" over the islets, prompting a coastguard ship to send a helicopter to send it away, according to multiple media reports.

Four Chinese Coast Guard ships entered the Senkaku, also known as the Diaoyu by Beijing, the disputed islets' territorial waters, and launched a helicopter into the islets' airspace, according to a statement from the Japanese Foreign Ministry.

Japanese Director-General of the Asian and Oceanian Affairs Bureau Masaaki Kanai summoned the Chinese embassy's Deputy Chief of Mission to express "strong protest" and "strongly urged" recurrence of such actions, it said.

China won’t step back

In response, China's Coast Guard (CCG) spokesman Liu Dejun said the vessels were there for a routine patrol "in accordance with the law" and that a Japanese civilian aircraft "illegally entered China's airspace" over the islets, prompting them to dispatch a helicopter to remove it, according to the state-run media Global Times.

“The Diaoyu Dao and its affiliated islets are China’s inherent territory. We urge the Japanese side to immediately cease all illegal activities,” the spokesman was quoted by the daily as saying.

“The China Coast Guard will continue to conduct rights protection and law enforcement operations in the waters and airspace of Diaoyu Dao to firmly safeguard China’s territorial sovereignty and maritime rights and interests.”