Holders of standard tickets will be allowed to visit the World Expo during the National Day holiday from Oct 1-7 if they pay an additional 40 yuan (US$6), the organizer said.

An official at the Expo bureau's Ticketing Center said they hoped the policy would prevent overcrowding over the final month as about 18 million standard tickets had yet to be used as of the end of August.

Seventeen days have been designated peak days, including the National Day holiday from Oct 1-7 and the last week of the Expo from Oct 25-31.

Only holders of peak-day tickets, which cost 200 yuan($29.87) each, are admitted on these days. Standard tickets cost 160 yuan($23.90).