MIAMI (AP) -- A scientist has been detained at the Miami International Airport after screeners spotted a metal canister in his luggage that looked like a pipe bomb, prompting an evacuation, a government official said.

The FBI and Miami-Dade police were interviewing the 70-year-old man, the official said Friday. No explosives have been found. The official spoke on condition of anonymity to discuss the ongoing investigation.

The man being questioned at the airport is an American citizen, FBI agent Michael Leverock said at a news conference in Miami.

"He's being very cooperative," Leverock said. "He's not under arrest at this time."

Leverock said the man was on a flight that flew into Miami but would not say where he flew from.

The item found in the man's luggage has been brought to a lab for more testing, Leverock said.

"We don't know if a crime has been committed here," he said.

A police bomb squad spent hours scouring the airport and passengers had to be evacuated from four of the airport's six concourses Thursday night and airport roadways were closed down, police and airport officials said. They described the shutdown of the concourses as a public safety precaution.

The airport fully reopened just after 4 a.m. Friday before the first scheduled morning departures, which signaled the start of the peak Labor Day weekend.

"Everything's back to normal," airport spokesman Greg Chin told The Associated Press soon after the closed concourses reopened.

He said the end of the evacuation order largely coincided with the nighttime drop-off in flights. Passengers, workers and others were allowed back in just as the airport was expecting the first of 1,500 passengers on flights between 4 a.m. and 6 a.m. alone -- and more thereafter.

The Miami International Airport Hotel, which is located near the airport's international terminal, was also evacuated, Chin said.

The Transportation Security Administration declined to identify the passenger, saying in a terse statement that the screener spotted something suspicious in a checked back at about 9 p.m. Thursday.

The federal agency responsible for air travel security said four of the six concourses in the 2-mile long complex -- Terminals E, F, G, and H -- had been evacuated beginning late Thursday.

Miami-Dade Police said a bomb squad spent hours at the airport with fire officials and the others. Fire trucks and police vehicles stood by and a hazardous material team was spotted at the scene.

Police spokesman Alvaro Zableta had urged those with scheduled departures Friday to check with local air carriers.

Chin said between 100 and 200 passengers were evacuated initially.

"I'm still not sure how many flights came in during this time, but any that did were relocated to the eastern or western ends of the airport," Chin said, adding parts of Concourses D and J remained open to flights while the evacuation order was in effect for remaining areas.

Lennox Lewis, was waiting to fly to Barbados later Friday morning in one of the four concourses that had been closed.

He said the Miami airport is "one of the most stringent" to get through because he has to be fingerprinted and have his picture taken at customs.

"Traveling right now is a pain but you have to do it. I don't get overly worried that people will do stupid things," said 39-year-old Lewis, who was flying with his two small children after a trip to North Carolina and Disney World.

Associated Press photographer Alan Diaz in Miami and Associated Press writers Eileen Sullivan in Washington and Bill Cormier in Atlanta contributed to this report.