Defence Minister David Johnston has rejected claims of a “secret” visit by Japanese submarine experts to a naval shipbuilding base in Adelaide.

The South Australian government says it was never informed about a Japanese delegation visiting the ASC facility at Osborne and it’s worried it could be part of an agenda to build the next generation of submarines overseas.

Mr Johnston confirmed on Wednesday that 16 Japanese submarine experts had visited the base but said the visit was linked to a broad bilateral agreement between the two countries.

“They’re down here looking at defence science and technology and we are discussing ways whereby we may both collaborate in that space to the mutual advantage of each of our countries,” he told ABC Radio.

The defence minister said the government was considering a range of options for the future submarine project before the release of a defence white paper next year.

Prime Minister Tony Abbott promised before the federal election that 10 new submarines would be built in Adelaide.

SA Defence Industries Minister Martin Hamilton-Smith said shipyards could be facing the same fate as Australia’s abandoned automotive industry.

“This is bigger than Holden for South Australia – it’s about the very survival of manufacturing,” he said in a statement on Wednesday.

Thousands of jobs and industry activity worth hundreds of billions of dollars hinged on the decision to build the new submarines in Adelaide, the minister said.

Federal Labor MP Mark Butler said it was extraordinary that the government had been “sneaking” in a Japanese delegation after promising to build the submarines in Adelaide.

Australian Manufacturing Workers Union national secretary Paul Bastian said importing submarines from Japan would destroy jobs and put national security at risk.