A Honolulu-bound United Airlines flight out of San Francisco has been stuck on the tarmac of San Francisco International Airport this afternoon, and the passengers "are ready to riot," said the husband of one of the passengers.

"They’ve been held prisoner for 24 hours — either on the plane or on the floor of the airport," said Honolulu attorney Michael Rudy.

His wife, Dr. Cheryl Lynn Rudy of Kapiolani Medical Center for Women & Children, is stuck on United Airlines Flight 73 and needs to get back to work to tend to patients Monday.

"They’re starting to riot on the plane," said Michael Rudy, who has been speaking to his wife on her cell phone. The crew is "trying to get them to remain calm."

But United Airlines spokeswoman Mary Clark said the passengers were inside the airport and not in the plane.

"They’re not on the plane," she said. "They’re in the airport and they can leave and do whatever they want for the next nine hours."

Dr. Rudy did not respond to repeated phone calls and texts to her cell phone.

The original 767-400 plane experienced "an aircraft maintenance issue," Clark said, and a replacement plane is en route to San Francisco from Honolulu.

The new flight Sunday is scheduled to leave San Francisco at 1:40 a.m. Monday and arrive in Honolulu at 3:50 a.m.

United Flight 73 is scheduled to depart San Francisco daily at 4:40 p.m.  and arrive in Honolulu at 6:59 p.m.

Dr. Rudy was among the passengers aboard United Airlines flight 73 on Saturday that never left, her husband said.

After three hours on the tarmac, Rudy said, the crew announced that it had a mechanical issue.

Passengers were finally removed from the plane after midnight and were given the option of taking a shuttle bus to a nearby hotel, which Dr. Rudy did, her husband said.

She and other passengers were told to meet the shuttle bus at 4 a.m. this morning.

But Dr. Rudy and the other passengers arrived at the airport today to find "no plane and no crew," Michael Rudy said.

"They waited for nine hours and finally boarded at 1 p.m. today," Rudy said. "They’ve been kept sitting on the tarmac for another 2 1/2 hours and they (United’s crew) won’t let them get off the plane. They were told there were problems with the luggage inspection, they’ve been told the plane is overweight."

"People are starting to riot. They won’t let them leave their seats."