The Obama administration announced Monday that more than 5 million people have signed up for new insurance plans under the health-care law, suggesting new momentum as the March 31 deadline for coverage this year approaches.

About 800,000 people have selected health plans on the state and federal insurance marketplaces this month, officials said in a blog post — almost as many as signed up during all of February. The figure brings the administration closer to Congressional Budget Office projections that 6 million people would enroll by the end of March.

Officials had predicted that the pace of enrollments would pick up this month, because March 31 is the last day to sign up for a marketplace plan and avoid a fine. The health law requires most Americans to have health insurance or incur a penalty of $95 or 1 percent of their income this year, whichever is higher.

Officials have not said how many of those who have enrolled have paid their initial premiums.