WELLINGTON, Fla. -- Investigators have opened a criminal probe into whether someone poisoned 21 polo horses that died during preparations for a match in the sport's top championship in Florida, officials said Tuesday.

The horses from the Venezuelan-owned team Lechuza Caracas were being unloaded from trailers at the International Polo Club Palm Beach when they began to appear dizzy, struggled to stand and fell to the ground. Veterinarians tried to help the horses, but one by one, they died.

"It was a horrific scene," said John Wash, president of the International Polo Club. "It was a scene that kept multiplying. It was, like, one right after another after another. It was like pulling up on a bus wreck or a plane crash."

State investigators believe the horses died from an adverse drug reaction or possibly toxins in their food or supplements.

“A number of the necropsies have been completed. These are very early results, very preliminary, and basically they found nothing to indicate an obvious cause of death," said Liz Compton of the Florida Department of Agriculture.

While state veterinarians run tests to determine what caused the deaths, law enforcement officers are looking into whether criminal negligence, or perhaps something more sinister, could have been involved, said a spokesman for the Department of Agriculture and Consumer Services.

"We want to make sure from a law enforcement standpoint that there was no impropriety ... no purposeful harm or laws violated in Florida," said department spokesman Terence McElroy.

Officials at the club hosting the U.S. Open tournament and several independent veterinarians have said the deaths appeared to be accidental, and investigators haven't identified suspects or foul play.

"We would be looking at any and all possible leads," said McElroy, whose department is leading the investigation with the help of the Palm Beach County Sheriff's Office.

Investigators from the Florida Department of Agriculture went to the Lechuza Caracas stables Tuesday afternoon.

“When you have a die-off of this magnitude, you are going to call in law enforcement, but right now they are merely fact finding," Compton said.

It may take weeks to complete toxicology testing to pin down the cause of what veterinarians believe was a swift toxic reaction that killed the horses, which were all from the Lechuza Polo team.

The deaths of the horses scheduled to play in Sunday's finals could have cost the team's owner, affluent Venezuelan businessman Victor Vargas, more than $2 million, with each horse estimated to be worth $200,000. However, the player-owner didn't stand to lose much in potential winnings, as purses in the sport played largely for pride rarely top a few thousand dollars. There is no purse in the U.S. Open.

Staff at the Lecuza Caracas barn on Tuesday did not want to discuss the case.

The tragedy also shocked Wellington, a town of horse clubs, training facilities, stables, polo grounds and wide-open fenced fields where the animals roam and graze along straight-line, neatly groomed streets.

"The players, the owners of the horses were in tears. Bystanders and volunteers were in tears. I mean, this was a very tragic thing," said Tony Coppola, 62, an announcer for the club, which hosts the tournament each year about 15 miles west of the millionaire enclave of Palm Beach.

On Monday, devastated horse lovers left flowers outside the stable's gate.

"It's very touching," Groom Anick Koziol said.

Koziol said that in his 16 years of working with horses, he has never heard of anything like it.

Lechuza Polo, a favorite to win the title at the event described as the sport's World Series, released a statement late Monday that the team does not know the cause of the deaths, but is helping with the investigation.

"This is tragic news. We are deeply concerned about the death of our ponies," the statement read. "We have never encountered such a dire situation like this as our horses receive the most professional and dedicated care possible."

Wash said doctors had ruled out any sort of airborne infection and that the tragedy was isolated to Lechuza's team.

He said games would resume on Wednesday, with the finals taking place Sunday. The Lechuza team has withdrawn.

While other equine sports, including hunting and jumping, have random drug testing, polo does not. Later this week, the U.S. Polo Association, the governing body of the sport, is expected to meet. An official told Local 10's Todd Tongen there is no doubt that random drug testing will be a topic of conversation.

"We would most likely take a zero-tolerance to that," Wash said. "Safety of the horse, safety of the rider comes first, and that is our main focus."