Competition between Hawaiian Airlines, Hawaii’s largest carrier, and Southwest Airlines, one of the U.S.’s top four carriers, is rising.

Hawaiian began daily nonstop service today between Maui and Sacramento getting a jump on a route Southwest Airlines is expected to announce shortly.

The new flight coincided with Hawaiian’s announcement that it would expand its code-share agreement with Virgin Australia broadening the network of flights between Hawaii and a dozen Australian and New Zealand cities. Hawaiian already provides non-stop flights to Hawaii from 12 U.S. mainland gateway cities, which will grow to 13 on April 4 when Hawaiian launches nonstop service from Boston. On average, Hawaiian also is flying 202 flights every day between the six populated islands in the Hawaiian archipelago.

By the end of May, Southwest already will have added 12 daily trans-Pacific flights to and from Hawaii and 16 interisland flights — adding 1,800 interisland air seats and 2,100 trans-Pacific air seats daily to the Hawaii market.

Southwest, which entered the Hawaii market March 17 with an inaugural flight between Oakland and Honolulu, is expected to start service between Oakland and Maui on April 7. Southwest begins flying between San Jose and Honolulu on May 5, and they’ll launch service between San Jose and Maui on May 26.

On April 28, Southwest starts interisland service which will run four times daily in each direction, between Honolulu and Kahului. On May 12 , the carrier will begin service between Honolulu and Kona flying planes four times daily in each direction.

Southwest is expected by month’s end to announce service between Hawaii and San Diego and Sacramento, and interisland service to Lihue.

However, the carrier will offer an entirely different product than Hawaiian, which will fly between Maui and Sacramento on its new fuel-efficient A321neo aircraft, offering 16 first class seats, 44 extra-comfort economy seats and 129 main cabin economy seats.

In contrast, Southwest’s customers will take the route on a Boeing 737-800, which offer 175-economy seats. Southwest customers don’t get to pick their seats before flights and there aren’t any red-eye flights. But Southwest allows passengers two free checked bags and two carry-on bags and doesn’t charge change fees.

The one commonality is that pricing has been increasingly competitive since Southwest filled a gap in its coverage, which didn’t extend to Hawaii— a favorite beach destination for the carrier’s California market.