Three big ships ran aground on a sandbank near the North Rhine-Westphalian city of Cologne on Monday, and were still there on Tuesday as experts tried to work them free, the water and shipping authority said.
One of the ships was carrying coal and a smaller ship has been allowed through the cordon to take some of its load, in a bid to make the larger ship lighter.
Attempts were made on Monday to drag the three ships off the sandbank with tug boats, but to little success. The Rhine is Germany's busiest river and a crucial trade artery for Europe.
According to regional newspaper the Westdeutsche Allgemeine Zeitung, river authorities were on Tuesday figuring out how deep the water was, and how deep it needed to be for the ships to be freed.
Diggers would then, the paper said, be brought in as quickly as possible to deepen the river.