Gary Melius, a well-known Long Island developer and prominent political patron, was shot in the head by a masked gunman on Monday in the parking lot of his opulent Gold Coast estate in Suffolk County, the police said.

The gunman fled and Mr. Melius was able to stumble back to his house, where his daughter saw him and rushed him to Syosset Hospital. He was later transferred to North Shore-Long Island Jewish Health System, where he underwent surgery Monday evening.

The police were still searching for the gunman, who they said they believed escaped in a car.

Mr. Melius, 69, who lives on the property, known as Oheka Castle, with his wife, also uses it as a high-end hotel, catering facility and wedding venue. At the time of the shooting, many people were at the house, including lunch patrons and workers.

One of the nation’s largest privately owned homes, Mr. Melius’s 109,000-square-foot French-style chateau has been the setting of some of the region’s most lavish nuptials, including former Representative Anthony D. Weiner’s wedding, which was officiated by former President Bill Clinton.