MIAMI — Park rangers discovered 20 "tar balls" on a Key West shore, prompting alarm Tuesday that the first sign of the massive BP oil spill had washed up on a Florida shore.

In Key West, the Coast Guard urged calm and sent samples of the three- to eight-inch flattened tar balls to a lab in Groton, Conn., to determine whether they had come from the massive leak in the Gulf of Mexico or perhaps oil remnants from a passing ship.

"The local people here are very sensitive to environmental issues so, of course, anything like this is going to cause concern," said Anna K. Dixon, a Coast Guard Navy lieutenant, junior grade, from Key West.

But she cautioned: "There is no proof or reason to believe these tar balls are from the Gulf (spill) at this point."

Analysis of the tar balls' origins would not be complete before day's end, she said, adding that the samples had been sent by overnight delivery.

She could not say the last time a concentration of 20 tar balls was found in Key West on a single day. The Coast Guard was sending searchers out — by land and air — to scout for more tar on Tuesday.

Still, the reports stirred alarm in the popular tourist destination.

"I woke up this morning and thought: 'Oh my god,"' said Sarah Notch, president of the Key West Attractions Association.

She spoke while working her day job: general manager of the Pirate Soul Museum in Key West.

For Notch, reports of nearly two dozen tar balls washing up on one of Key West's most popular attractions dramatically upped the stakes in an oil spill that had seemed threatening but still far away.

"I was going over this in my head last night," she said of the oil-spill scenarios that might touch Key West. "I said, 'Well, we still don't know."'

A pristine beach is Fort Zachary Taylor State Park's main selling point. The recorded message that greets callers states: "If you're looking for Key West's best beach, you've found it." Park rangers at Fort Zachary Taylor and the adjacent Navy beach at Truman Annex in Key West discovered the tar balls throughout the day Monday, according to a Coast Guard statement, and alerted pollution control experts about 5:15 p.m.

The heaviest concentration was found at high tide, about 12:30 p.m.

More surveys were planned for Tuesday morning with participation of the Coast Guard, National Oceanic and Atmospheric Administration and Florida Keys National Marine Sanctuaries. The Coast Guard also said it would send a helicopter "with a trained pollution investigator on board" to do more searches.

Meanwhile, BP announced it was awarding tourism grants to the governors of Florida, Alabama, Mississippi and Louisiana to help promote tourism over the coming months, in the wake of the Deepwater Horizon spill.

BP said it would give $25 million to Florida and $15 million each to Alabama, Mississippi and Louisiana.

Florida Gov. Charlie Crist said he would use the funds "to spread the word that Florida's beaches are clean, our fish are biting, and the Sunshine State is open for business."