All the nine injured in the Monday night shooting are in stable condition. A male and a female, both adults, were the deceased victims, a police officer told a media briefing, Reuters reported.
A large number of adults were present at the park, according to the police.
"We have not recovered any weapons at this time," the officer said. No arrests have been made.
"This is significant. It's Memorial Day... we understand the significance of this event and we will make sure to provide an update on Tuesday."
Memorial Day, traditionally observed on the last Monday of May, is a federal holiday in the United States dedicated to honoring and mourning military personnel who have died in the performance of their duties.