Yonhap said police had secured warrants for the arrest of two union leaders involved.

BBC: South Korea police break up Yoosung Hyundai strike

The South Korean news agency Yonhap said that two warships equipped with Aegis defence systems would monitor the situation.

BBC: South Korea 'deploys warships to track North missiles'

The Yonhap news said it was expected to make contact with its ground station at 05:00 on Thursday, at which point its operators will be able to make the final judgement on whether the launch achieved its goals.

BBC: South Korea launches space rocket carrying satellite