Clouds are gathering on the horizon for Japanese carmakers, their business outlook put at risk by the new coronavirus from China as it threatens to cripple their supply chains in the country, now a global manufacturing powerhouse.

While automakers have been struggling to assess how the outbreak of the pneumonia-causing virus will affect their production and sales, one thing is clear — they will face significant impacts if the situation continues.

"To be honest, it's impossible to manufacture cars without China," said Toshiaki Okada, chief financial officer at Subaru Corp., at a news conference Wednesday.