NEW YORK – Police found an "amateurish" but potentially powerful bomb in a smoking sport utility vehicle in Times Square, then cleared the streets of thousands of tourists milling through the landmark district so they could dismantle it, authorities said Sunday.

"We avoided what we could have been a very deadly event," Mayor Michael Bloomberg said. "It certainly could have exploded and had a pretty big fire and a decent amount of explosive impact."

Investigators removed three propane tanks, fireworks, two filled 5-gallon gasoline containers, and two clocks with batteries, electrical wire and other components from the back of the Nissan Pathfinder, Police Commissioner Raymond Kelly said. A black metal box resembling a gun locker was also recovered and will be detonated off site, he said.

Bloomberg called the explosive device "amateurish" and Kelly said the explosives were consumer-grade fireworks but could have caused huge damage on a block of Broadway theaters and restaurants teeming with tourists.

"I think the intent was to cause a significant ball of fire," Kelly said.

No suspects were in custody, although Kelly said a surveillance video showed the car driving west on 45th Street before it parked between Seventh and Eighth Avenues. Police were looking for more video from office buildings that weren't open at the time.

A white robotic police arm broke windows of the black Nissan Pathfinder to remove any explosive materials after a T-shirt vendor alerted police to billowing smoke coming from the back of the vehicle at about 6:30 p.m. Heavily armed police and emergency vehicles shut down the city's busiest streets, teeming with taxis and theatergoers on one of the first summer-like days of the year.

A Connecticut license plate on the vehicle did not match up, Bloomberg said. Police interviewed the Connecticut car owner, who told police he had sent the plates to a nearby junkyard, Bloomberg said.

After the vendor noticed smoke coming from the SUV, police cleared buildings and streets at the so-called "Crossroads of the World"; the south tower of a Marriott hotel was evacuated and several blocks surrounding Times Square remained closed hours later. Officers were deployed around the area with heavy weapons on empty streets in the heart of busy midtown Manhattan.

Shelly Carlisle, of Portland, Ore., said police crowded into her Broadway theater after the curtain closed on "Next to Normal," a show on the same block where the SUV was found.

"At the end of the show, the police came in. We were told we had to leave," Carlisle said. "They said there was a bomb scare."

The car was parked on 45th Street, and the block was closed between Seventh and Eighth avenues as a precaution, police said. Times Square lies about four traffic-choked miles north of where terrorists bombed the World Trade Center in 1993, then laid waste to it on Sept. 11, 2001.

The block that was closed is one of the prime blocks for Broadway shows, with seven theaters housing such big shows as "Billy Elliot" and "Lend Me a Tenor."

The curtain at "God of Carnage" and "Red" opened a half-hour later than usual, but the shows were not canceled, said spokesman Adrian Bryan-Brown.

Katy Neubauer, 46, and Becca Saunders, 39, of Milwaukee, were shopping for souvenirs two blocks south of the SUV when they saw panicked crowds.

"It was a mass of people running away from the scene," Neubauer said.

Said Saunders: "There were too many people, too many cops. I've never seen anything like it."

Bloomberg left early from the White House correspondent's dinner Saturday night. President Barack Obama, who attended the annual gala, praised the quick response by the New York Police Department, White House spokesman Nick Shapiro said.

He has also directed his homeland security and counterterrorism adviser, John Brennan, to advise New York officials that the federal government is prepared to provide support.

Brennan and others will keep Obama up to date on the investigation, Shapiro said.

The FBI Joint Terrorism Task Force in New York responded along with the NYPD, said agent Richard Kolko.

"We have no idea who did this or why," the mayor said Sunday, but said that the city is always a top terrorism target. The latest threat came last fall when air shuttle driver Najibullah Zazi admitted to a foiled homemade bomb plot aimed at the city subway system.

"These things invariably ... come back to New York," Bloomberg said.

Officials said the device found Saturday was crudely constructed, but Islamic militants have used propane and compressed gas for years to enhance the force of explosives. Those instances include the 1983 suicide attack on the U.S. Marines barracks at the Beirut airport that killed 241 U.S. service members, and the 2007 attack on the international airport in Glasgow, Scotland.

In 2007 the U.S. military announced that an al-Qaida front group was using propane to rig car bombs in Iraq.

Times Square has been a frequent target, if not for potential terrorists, then for rabble-rousers.

In December, a van without license plates parked in Times Square led police to block off part of the area for about two hours. A police robot examined the vehicle, and clothes, racks and scarves were found inside.

In March 2008, a hooded bicyclist hurled an explosive device at a military recruiting center in the heart of Times Square, producing a flash, smoke and full-scale emergency response. No suspect was ever identified.

In December, police evacuated thousands of holiday tourists from Times Square after finding a white van that had been parked there for days without license plates and blacked-out windows. No bombs were found, and police later said they overlooked the van because it contained a parking placard for a nonprofit police group.

Police have spent years trying to crack down on street hustlers and peddlers preying on tourists. But there have been two major gunfights in recent months. A street hustler armed with a machine pistol exchanged shots in December, shattering a Broadway theater ticket window, before police fatally shot the man.

Four separate instances of shootings and more than 50 arrests on a mile-long stretch of Manhattan last month around Times Square prompted the mayor to call the mayhem "wilding."

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Contributing to this report were AP Washington bureau chief Ron Fournier, and Associated Press writers Eileen Sullivan and Pete Yost in Washington, Michael Kuchwara in New York and Robert H. Reid in Kabul.