Hannah Green's first title defence on the LPGA Tour will have to wait another day.

Poor air quality in Portland, Oregon has forced the tour to defer the tournament a day in the hope that the air clears.

It will now be a 54-hole tournament starting on Friday.

Australia's Green won the Portland Classic last September, her second win of the 2019 season.

She is scheduled to defend her major championship win at the Women's PGA Championship in Pennsylvania next month.

The air pollution problem in Portland has been caused by fires in Oregon, Washington and California.

The Columbia Edgewater Country Club was closed on Monday and Brooke Henderson, the Canadian who almost won in California last week, withdrew because of the smoke.

“Our meteorologist says that it is unlikely that air-quality conditions will improve before midday Thursday, and we cannot risk the health of our players, staff, volunteers, broadcast crew and others at the golf course," LPGA chief tour operations officer Heather Daly-Donofrio said in a statement. “This is not a choice we made lightly, but we are confident that this is the right decision.”

Green, 23, is one of six Australians in the field this week. The others are Minjee Lee, Su Oh, Sarah Kemp, Sarah Jane Smith and amateur Gabriela Ruffels.