Smoke from Canadian wildfires triggered a fresh wave of disruption across American sports on Thursday, forcing more postponements and jeopardizing Saturday's scheduled horse racing showpiece, the 155th Belmont Stakes.

Air quality alerts were raised along the US East Coast as New York's Belmont Park called off Thursday's races and the Washington Nationals postponed their Major League Baseball game against visiting Arizona to June 22 due to "poor air quality."

New York governor Kathy Hochul warned the Belmont Stakes would be canceled if air quality is too unhealthy.

"We hopefully can get this going, but there's no assurance of what the weather is going to be, so it's going to be a last-minute decision, I'm sure," Hochul said.

Hochul said "enhanced measures" have been instituted to protect horses, riders and spectators.

The Belmont Stakes would be canceled if the air quality index at Belmont Park is beyond 200, considered very unhealthy. If the index ranks between 150-200, horses would need to pass a pre-race veterinarian exam to compete.

There were optimistic signs on Thursday as Major League Baseball's New York Yankees played a double-header against the Chicago White Sox after a Wednesday game was postponed due to the smog.

The air quality index at Yankee Stadium on Wednesday had been at 335, a hazardous level.

The New York Racing Association (NYRA) shelved racing at Belmont Park on Thursday after morning workouts were canceled, including those for the nine horses set to race in Sunday's 1 1/2-mile, $1.5 million Belmont Stakes.

"Safety is paramount as we navigate this unprecedented situation," said NYRA president David O'Rourke. "NYRA will actively monitor all available data and weather information as we work toward the resumption of training and racing.

"Based on current forecast models and consultation with our external weather services, we remain optimistic that we will see an improvement in air quality on Friday."

Live racing was set to resume on Friday but there were safety fears as a thick, orange haze engulfed New York.

Horse safety has been under scrutiny during this year's Triple Crown run after the Kentucky Derby was clouded by a spate of deaths at Churchill Downs that included two on Derby day and eight within three weeks.

At last month's Preakness in Baltimore, Havnameltdown suffered a catastrophic front left leg injury during the sixth race of the day and had to be euthanized on the track at Pimlico Race Course.

- NFL practices go inside -


NFL teams were also forced to alter their off-season training workouts Thursday due to air quality concerns, with the New York Giants calling off a session in an indoor facility, saying conducting the workout wasn't worth the risk.

The New York Jets, Baltimore Ravens, Philadelphia Eagles and Washington Commanders all moved Thursday practices inside due to poor outdoor air quality.

Smog caused by wildfires in Canada shrouded multiple northeastern US cities this week.

On Wednesday, fixtures in MLB, the Women's NBA and National Women's Soccer League were all disrupted.

MLB also postponed Detroit's game at Philadelphia on Wednesday due to air quality.

The NWSL's NJ/NY Gotham FC home match against the Orlando Pride in Harrison, New Jersey, was postponed until August 9 due to the New York metro area air quality concerns.

"The safety of our players, officials and fans is our top priority," the NWSL said in a statement. "Following consultation with the NWSL medical and operations staff, it was determined that the match could not be safely conducted based on the projected air quality index."

Even indoor events were delayed, with the WNBA New York Liberty's home game in Brooklyn against the Minnesota Lynx postponed due to air quality issues.