Olympic surfing chiefs have scrapped the final day of competition to cram medal events into Tuesday's schedule while big waves last, as a tropical storm approaches Japan.

Tropical Storm Nepartak is set to whip up ideal surfing conditions on Tuesday at Tsurigasaki Beach, 100 kilometres (60 miles) east of Tokyo.

But the big waves are likely to have disappeared by Wednesday -- when the medal events were due to be held.

Organisers announced on Monday that the quarter-finals, semi-finals and medal events of the men's and women's competitions would all now be held on Tuesday.

The International Surfing Association's technical director had "assessed the overall impact of the surf forecast on the final day of competition and adjusted the schedule accordingly," organisers said in a statement.

The competition was originally scheduled to be held over four days, with an extra four days in reserve in case weather conditions made them necessary.

Surfers have found the waves at the Games bigger than they were expecting.

"As soon as you say Tokyo 2020 in August, everyone says you're going to surf knee-high waves," American surfer Kolohe Andino said on Monday.

"And of course, the very first few days it's waves that are... head-high waves. It's funny, that's how surfing is. You've got to be prepared for everything."

Olympic organisers opted to hold the event at Tsurigasaki Beach instead of using an artificial wave pool.