A two-alarm fire damaged an apartment complex in Brookline Thursday morning, officials said. The fire started in the basement of the building at 669 Washington St. around 4 a.m. and spread to the upper floors, officials said. The cause is under investigation. No one was injured. Washington Street was closed from Beacon to Cypress streets until 8 a.m. while the fire was brought under control. A senior center on Winchester Street was opened to serve as an emergency shelter for the 17 displaced residents, said Lieutenant Philip Harrington of the Brookline police. Some were allowed back into the building to gather some belongings, Harrington said. Volunteers provided 10 people with emergency funds for food and clothing and provided seven with a hotel stay, officials said.