United Continental Holdings shares surged Wednesday after the airline posted stronger revenue and profits than Wall Street expected in the fourth quarter, while issuing a sunny outlook for earnings growth in 2019.

The company's shares were up more than 7 percent in morning trading Wednesday.

United's unit revenue, a measure of how much an airline makes for each seat it flies a mile and a gauge of airfares, rose 5 percent in the fourth quarter from a year earlier, at the high end of the company's estimate. The airline said revenue grew in each of the regions it operates, while domestic revenues grew at the fastest clip: 12 percent.

The results, which the airline released on Tuesday after the market closed, represent a sharp turnaround for United. A year ago, United CEO Oscar Munoz struggled to persuade investors the company's plan to expand as much as 6 percent a year would pay off. But the airline has topped earnings estimates and plans to continue with capacity expansion of as much as 6 percent in the first quarter.

The Chicago-based airline said it expects unit revenue to be flat to up 3 percent in the first three months of this year from the same period in 2018.

The parent company of United Airlines said revenue in the last three months of 2018 was $10.49 billion, higher than the $10.34 billion analysts polled by Refinitiv were expecting. Net income, however, fell 20 percent from a year earlier to $462 million, as costs rose. United said its fuel bill in the fourth quarter was 27 percent higher than a year earlier.

In the first quarter of 2019, United expects to post earnings of $1 a share on an adjusted basis, above analysts' estimates of 84 cents.

Its per-share earnings in the quarter were $2.41 on an adjusted basis, compared with the $2.04 that was expected.

Earlier Tuesday, Delta Air Lines said it expected its unit revenue to grow by a maximum of 2 percent in the first quarter due to the U.S. partial government shutdown and the timing of the Easter holiday in the second quarter.

United's Munoz on Wednesday said the company isn't seeing a "significant" impact on reservations.

"There is some impact there," Munoz told CNBC's Phil LeBeau in an interview. "It's not discernible and it's not significant. Clearly the longer this goes, of course there's going to be impact, and we do worry about that."

United expects to earn between $10 and $12 a share on an adjusted basis this year, in line with estimates.

The airline's executives will hold a call with analysts at 10:30 a.m. ET on Wednesday.