The vessels, registered in Qinhuangdao, China, were believed to be sailing toward Mauritania in northwestern Africa to fish but had to stop and anchor off Johor due to a malfunction, the Malaysian Maritime Enforcement Agency said in a statement Saturday evening.

There were six captains and 54 crew members, all Chinese nationals and between the ages of 31 and 60, it said.

All were arrested after failing to produce permits from authorities to conduct activities or anchor in Malaysian waters, the agency said. It added the vessels, which didn’t have any cargo, were seized.

Territorial tensions in the South China Sea have been on the rise with countries such as Vietnam pushing back against China’s maritime claims.

Malaysia recently joined the fray by submitting to the United Nations its claim to rights over the remaining portion of a continental shelf beyond 200 nautical miles from the country’s baselines.