The Obama administration says sign-ups picked up last week under the president's health care law.
More than 618,000 people selected a plan for 2015 from Nov. 29 through Dec. 5, the Health and Human Services department reported Wednesday.
It was the highest weekly number since open enrollment began Nov. 15.
Sign-ups were about evenly split between new customers and consumers making changes to existing coverage.
Cumulatively, nearly 1.4 million people have enrolled through HealthCare.gov, the online market that offers subsidized private insurance in 37 states. Statistics for states running their own websites will be reported later.
The administration set a target of 9.1 million people enrolled across the country for 2015. That includes 6.7 million current customers, most of whom will be automatically re-enrolled.
Sign-up season runs through Feb. 15.