The move takes to 24.5 million the total number of vehicles recalled by Honda due to the issue.

A spokesman in Tokyo for the carmaker told AFP news agency on Thursday that the carmaker had found some airbag inflators had "uneven gas density, which we worry could do some harm".

"It is a preventive measure and unlike other normal recalls we are not waiting for the full results of the research," he said.

According to reports, Honda has said that of the latest 4.5 million vehicles involved in the recall, 1.63 million are in Japan, whilst North America and Canada are not included.

The latest news comes a day after Honda said an X-Trail sport utility vehicle fitted with a Takata airbag had exploded last month on a Japanese highway, causing a fire and marking the carmaker’s first case of injuries sustained from the airbag issue.

The driver's left cheek was lightly burnt, although it is unclear whether this was caused by the explosion.

According to reports, the vehicle had been recalled in April 2013 and the driver had been sent reminders to take action.