On Thursday, Sweden and several other northern European countries closed their airspace.
On Friday, the civil aviation authority in Stockholm said Swedish airspace "is now reopening step by step." It said flights will resume in northern Sweden, with restrictions being lifted throughout the country gradually.
Norwegian airport operator Avinor reopened airspace over the northern half of Norway's west coast at 0700 GMT.
In Denmark, aviation officials said the airspace will stay closed at least through 0600 GMT Saturday.
Finland, which closed its airspace early Friday, said it would extend the measure to Sunday afternoon instead of Saturday, as earlier planned. Finnish airports operator Finavia Corp. said it expects the volcanic ash plume to remain over the country for several days.