DALLAS — Southwest says it has mostly fixed computer problems that caused hundreds of flights to be canceled, but it is telling passengers to get to the airport early because there could be long lines.

The airline has already canceled more than 300 flights on Thursday.

The airline said that it was trying to accommodate stranded passengers on new flights. Because of that, it expected long lines and told passengers to arrive early for Thursday flights.

Southwest operates daily, direct flights out of Long Island MacArthur Airport to four Florida cities and Baltimore-Washington International Airport. The airline also flies out of LaGuardia and Newark airports.

Several of the airline’s technology systems were affected by an outage that started Wednesday afternoon, causing the cancellation of nearly 700 flights and delays for hundreds more.

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Southwest’s website crashed, and the airline briefly held up all departing flights on Wednesday.

Southwest says in a statement that most systems are back online.

With Gary Dymski