Trump was unable to join other spouses for a tour of Hamburg's harbor, which was expected to precede a visit to a climate research center. The venue for the second part of the gathering had to be changed, due to traffic blockades mounted by the protesters.
Stephanie Grisham, the first lady's spokeswoman, said police were unable to secure the surroundings to allow Trump to leave.
“She was prevented from participating in today's spousal program, which she was looking forward to,” Grisham said in a statement.
Trump herself tweeted well-wishes for those injured in widespread demonstrations across the German port city, where two days of summit meetings began Friday.
Abby Phillip contributed to this report.