The first event was the women's long jump, followed by the 100-metre dash segment of the men's decathlon and the men's shot put.
Finnish fans were particularly eager for the men's javelin event. Javelinists Tero Pitkämäki and Ari Mannio were joined by Teemu Wirkkala. He was an eleventh-hour replacement for Antti Ruuskanen, who is out with pneumonia.
Mannio threw a season-best toss in the javelin qualifier, while Finland's Sanni Utriainen made it into the women's javelin final.
The forecast called for showers and possible thunderstorms through much of the day in Helsinki, with strengthening winds and highs of 15 to 21 degrees Celsius.
Tuesday evening's opening ceremony attracted some 15,000 people to Helsinki's Senate Square for an evening extravaganza featuring dance and music from rock band The Rasmus and reggae star Jukka Poika.
Ticket sales have been sluggish so far. Some 120,000 tickets have been sold, but that is just 60 percent of target number, says Esa Honkalehto, secretary general of the Helsinki games.
Lemaitre gears up for London in Helsinki
Among those poised for the start of the action is Christophe Lemaitre, seen as Europe's biggest hope of breaking Jamaican and US sprinting dominance at this summer's Olympics. He will continue his training for the London Games at the European Championships on Wednesday.
It was during the 2010 continental edition in Barcelona that the 22-year-old French athlete sprinted into the limelight and he admitted that expectations are far higher as he comes into the 2012 championships.
"I've moved out of the shadows into the light," he said of his profile since winning a surprise three gold medals in Barcelona two years ago over 100m, 200m and 4x100m.
On Wednesday he easily won his heat in the men's 100-metre dash.
Meanwhile Finland's Sami Itani turned in a personal-best time in the decathlon 400 meters.
The championships run through Sunday.
Yle is broadcasting the track and field action on TV1 and TV2 as well as on radio and online.