Thousands of southern Nevadans evacuated their homes, and this city of 70,000 was virtually shut down Monday following the pre-dawn leak of chlorine gas at a chemical plant.

At least 29 people sought treatment at St. Rose De Lima Hospital, but no serious injuries were reported. Others stopped in at fire stations complaining of shortness of breath and were given oxygen by firefighters.Janet Smith, a spokeswoman at Mercy Ambulance, said the company received 110 calls over a six-hour period and most were people suffering the effects of the chlorine gas.

The leak was reported about 2:30 a.m. and was halted at 8 a.m., according to Fire Department spokesman Bob Leinbach. He said there were no serious injuries.

"We might just dodge the bullet on this one," Leinbach said.

Clark County Manager Pat Shalmy said authorities were treating the spill as a "very serious emergency."

Streets and roads in and out of the city were closed, including U.S. 93 and 95. Nevada Highway Patrol spokesman Phil Dart said they would be reopened when authorities felt it was safe to enter the city.

Schools throughout the city were closed, and two facilities were turned into shelters for evacuees, with cots and mattresses spread across gymnasiums at the schools.

Joe Mack, a newsman for KXTZ radio, said there was a greenish cloud over the city of Henderson just after dawn.

"It's real eerie on the streets because most of the businesses are closed," said Mack, whose studio is located in Henderson.

Ironically, the leak came just after the third anniversary of massive explosions at the nearby PEPCON plant. The May 4, 1988, explosions killed two people, injured more than 300 and caused $74 million in property damage in the Henderson area.

Mack said there have been previous chemical leaks at the plant, which produces chlorine for swimming pools. He said there's been nothing as serious as today's leak.

One police official told Mack "If you can smell it strong enough, get out."

Clark County officials say seven firefighters were taken to St. Rose De Lima Hospital for treatment after inhaling the gas.

Firemen who responded to the scene were decontaminated later in the morning at a control point some distance from the plant.

Women and children patients at St. Rose De Lima were evacuated to Sunrise Hospital, according to Las Vegas Metro Police.

Metro reported the Henderson Police Department had closed its communication center because of the effects of the spill.

Many residents were evacuated in buses provided by the Clark County School District.

The leak occurred at the Pioneer Chemical plant on Lake Meade Drive at about 2:30 a.m., Leinbach said. The spokesman said he was not sure how the leak was first discovered.

Henderson is approximately 10 miles south of Las Vegas.