Five workers were missing Tuesday after an undersea tunnel collapsed as it was being constructed at one of Japan's largest oil refineries, emergency services and reports said.
Local media said divers were being sent to the site in Kurashiki, where firefighters confirmed to AFP they were dealing with an incident at the site, which lies around 550 kilometres (350 miles) west of Tokyo.
"We received a report that an accident occurred at the No. 2 undersea tunnel in the port of Mizushima, involving six workers," said a spokesman for the Kurashiki City fire department.
"One of the six got out but the five others are missing," he said without disclosing further details.
Jiji Press said the accident happened at an oil refinery operated by JX Nippon Oil and Energy Corp.
NHK said seawater may have poured into the tunnel and police are sending divers to the accident site.