The Japan Coast Guard on Sunday started safety checks on the suspected North Korean spy ship salvaged Wednesday from the East China Sea.
A full-scale probe is scheduled for around Friday, coast guard officials said.
About 40 coast guard workers, including explosives experts, began safety checks from 9 a.m. The ship is sitting in a water-filled tank on a barge anchored some 3 km from the port of Kagoshima.
The coast guard plans to take until about Friday to check for the presence of dangerous material in the ship while gradually draining water from the tank.
The ship will then be brought ashore and placed in a private dock for further investigation, the officials said.
The 100-ton-class ship sank in China's exclusive economic zone about 390 km from the island of Amami-Oshima on Dec. 22 after exchanging gunfire with coast guard vessels.
The coast guard discovered various types of weapons, including antiaircraft missiles, and rocket launchers, at a depth of 90 meters on the seabed where the ship went down.
Japan believes the ship was a North Korean vessel involved in espionage or drug-running. North Korea denies the allegations.