Monday is the sign-up deadline for health insurance coverage that will start Jan. 1.
The Obama administration announced it was extending the federal deadline by a day through Tuesday, but this does not affect Covered California, which is California's own health insurance exchange under the federal Affordable Care Act. The state had extended the previous enrollment deadline from Dec. 15 to Monday.
Between 10 a.m. and 11 a.m., there were 1.3 million page views on the website, and due to the tremendous volume, some pages took longer to load, an official said. By 6 p.m., most users were unable to access the application online.
Due to technical issues, the agency said they will institute a "grace period" for those who attempted to get coverage but were unable to sign up.
"We're going to help people get across the finish line," said Executive Director Peter Lee.
It was unclear when the grace period would end, but Lee said the agency's goal was to have an insurance policy in place for everyone who "made a good faith effort" to get one by Monday's deadline.
Preliminary numbers show that more than 400,000 California residents have enrolled in healthcare plans, officials said. Those who enroll by midnight will have until Jan. 6 to pay for policies starting in 2014.
Anyone who signs up during the last three months of the initial Covered California open enrollment period, which is Jan. 1, 2014, to March 31, 2014, will receive coverage the following month, as long as the person's full premium payment is received.
Those who do not sign up for health insurance by March 31, 2014, will face a penalty. For individuals, the penalty is $95 or 1 percent of income, whichever is greater. For families, the penalty is $95 per uncovered adult and $47.50 per uncovered child (up to $285), or 1 percent of the family's income.
The Associated Press contributed to this report.