Worsening smog in Singapore prompted swimming World Cup organizers to cancel 15 finals races just an hour before the session was to start.

Singapore has been shrouded with smoke and haze from Indonesian forest fires for weeks.

Organizers from FINA, the International Swimming Federation, scrapped the races — which included a closely-watched women's 200-meter backstroke final — as the Pollutant Standards Index, or PSI, the country's main measure of air pollution, climbed toward 200.

The morning session of heats was held as planned, and two more sessions Sunday were scheduled to go ahead.