LAS VEGAS — High concentrations of a chemical similar to bleach seeped into a pool at the MGM Grand on the Las Vegas Strip on Friday, causing hotel officials to evacuate some 1,500 guests and sending at least 26 people to local hospitals with breathing problems.

Richard Brenner of the Clark County Fire Department said sodium hypochlorite went into the hotel's lazy river pool when a valve used to the control the chemical malfunctioned and remained on.

"People started smelling chlorine," Brenner said. "It doesn't take much to set our nose off."

About 100 people had trouble breathing but did not need to go to hospitals, said Brenner, the department's hazardous materials coordinator.

Brenner said he thought everyone would be OK. Those treated needed to breathe from oxygen tanks to get the chemicals out of their lungs, he said.

Bryce Baril, 32, of Seattle, said he and his wife were preparing to go into the pool when a woman announced over the intercom that he and others needed to go to another pool. A few minutes later, she told everyone to leave all the pools, he said.

"We got up to the exit and in comes the hazmat or the fire department, breathing through their masks," Baril said. "We never smelled anything but we were supposedly right where it was."

The couple was in Vegas to celebrate their 10th wedding anniversary.

Brenner said the chemical went into the water and into the air, but fire officials determined less than three hours later that the area was OK and turned it back over to the hotel's owners, MGM Resorts International.

Hotel officials were letting evacuated guests come back to the pool area to retrieve their belongings and the pool was expected to reopen later in the day, said MGM Resorts International spokesman Gordon Absher.

Spring Valley Hospital spokeswoman Naomi Jones said five patients taken there were all in good condition.