The oil comes from the tanker Baltic Carrier, which was holed in a night-time collision with a freighter near Falster late on Wednesday night.
Seabirds and ducks have been found dead and dying in the slicks, which have washed ashore onto Moen, Bogoe and Falster islands off southern Denmark.
But the authorities say they remain confident that most of the slick can be contained.
The oil comes from the tanker Baltic Carrier, which was holed in a night-time collision with a freighter near Falster late on Wednesday night.
At least 1,900 tonnes of its 33,000-tonne cargo leaked into the Baltic, and was broken into small slicks by gale-force winds.
Officials say some of the oil nearest the coast has been swept into relatively calm waters in the Groensund strait, where it may be relatively easy to scoop up.
Oil-coated birds, including several dead ducks, were seen on Bogoe island; others were struggling to escape five-centimetre (two-inch) deep oil along the shore.
At sea, a small fleet of boats from Denmark, Sweden and Germany is fighting to stop the slicks spreading.
Naval officer Jens Hylsted said on Friday that most of the oil was still away from the coast, and calmer seas were helping the clear-up operation.
"The situation is developing positively. Let's hope the weather remains clement," he said.
The remaining oil in the damaged compartment has been pumped into undamaged parts of the tanker, according to German coastguards.
German officials said the Marshall Islands-registered tanker was at anchor and in no danger of sinking.
The freighter that it collided with, the Cypriot-flagged Tern, is also still seaworthy and has sailed into a German port. It was carrying a cargo of sugar from Cuba to Latvia.
The area last experienced a serious oil spill in 1985, when about 300 tonnes of oil reached the shores of Laesoe island, halfway between the peninsula of Jutland and western Sweden.