Perth Airport passengers are being warned they may face delays at peak times over the next six months due to one of its runways being closed for repairs.

The airport says the closure was necessary because maintenance staff noticed cracks on the runway.

The Executive General Manager of Operations at Perth Airport, Peter Cock, has told the ABC's Morning program, the changes will only affect some flights.

"When it will make a difference is if it's arriving from the north so coming in over South Guildford and Bellevue , so then arrival rates will drop from 26 an hour to 24 an hour," he said.

"To give some context, when it's hazy like today the arrival rate is set at 20 an hour.

"You won't notice it any more than you would due to climatic conditions or due weather conditions."