Preliminary heats will be held in multiple events, including women's triple jump, women's 100, women's discus, women's 400, men's 400 hurdles, men's hammer throw, men's 3000 steeplechase, men's long jump, and men's 1,500.
Round one heats in the women's 100 begin at 2:05 p.m. The American to watch is Carmelita Jeter, the top U.S. sprinter in the 100.
British golden girl Jessica Ennis made a blistering start in the heptathlon in front of a sell-out crowd of 80,000.
With a vociferous home crowd roaring her on, Ennis clocked the best time ever recorded in the 100m hurdles discipline.
The 26-year-old flew over the barriers flawlessly in a superb 12.54sec, shaving 0.25sec off her best and equalling the winning time of American Dawn Harper in the individual event at the 2008 Olympics.
She went on to clear 1.86m in the high jump to put her in the lead after two events of the seven events, with the shot put and 200m to come later Friday.
"I'm still in shock from the hurdles, to be honest," Ennis said. "I can't believe I ran that time. It was a great start."
Two medals will be decided in the evening action, the women's 10,000m and the men's shot put.
To watch the event live click here.
