Many HealthCare.gov customers will face higher costs next year, the Obama administration acknowledged Thursday in a report that shows average premiums rising modestly.

However, officials said millions of consumers who are currently enrolled can mitigate the financial consequences if they are willing to shop around for another plan in a marketplace that's becoming more competitive.

Premiums for the most popular type of plan will go up an average of 5 percent in the 35 states where the federal government is running the health insurance exchanges, said a report from the Health and Human Services Department.

However, the administration says about two-thirds of current customers can still find coverage comparable to what they have now for $100 a month or less if they shop around. That estimate takes into account the tax credits that most consumers are entitled to, which cover about three-fourths of the cost of premiums on average.

Double-digit premium increases were common for people buying their own insurance before the passage of President Barack Obama's health care law.

The modest average increases the administration reported Thursday mask bigger price swings from state to state, and even within regions of a state. Some are still seeing double-digit hikes. But others are seeing decreases. And most are somewhere in the middle.

On the whole, administration officials say the market is more stable.

"In today's marketplace, (insurers) are competing for business," Health and Human Services Secretary Sylvia M. Burwell said in a statement. "Returning customers may find an even better deal if they shop and save."

The report said about 90 percent of customers will have a choice of three or more insurers this year, with each company usually offering a range of plans. That's a notable improvement from last year, when 74 percent of customers had similar options.

The most popular coverage is known as the lowest cost silver plan and will go up 5 percent next year.

Another key plan, the second-lowest cost silver, will go up an average of 2 percent.

Obama's health care law offers subsidized private health insurance to those who don't have coverage on the job. Online markets called exchanges provide different options in each state.