Shanghai Expo organizers will launch a comprehensive public transport network combining subway, bus and marine services to provide convenient access to the 3.28 square kilometer park for nearly 70 million visitors.

Officials described the scale of the operation as unprecedented for a World Expo.

"The transport network, including one subway line, five bus lines and 12 water traffic lines, is the largest ever," said Zhou Huai, deputy director of the Urban Transport Management Bureau in a press conference Saturday.

The transport system, which is set to open May 1, will give access to 95 percent of the expo park with no more than 300 meters between stops.

The subway line to the expo park includes stops at Madanglu Road, Lupu Bridge and World Expo Avenue.

It runs from 9 am to 12 pm, with a service frequency of between three to six minutes and a capacity for 25,000 to 47,000 visits per hour.

Up to 120 electric buses will operate on the Yuejiang Line and will have power to run for 100 kilometers on a full load. The line is seven kilometers' long with five stops, connecting Pudong and Puxi Park.

The 12 water traffic lines are divided between ferry services for individual tourists and some exclusively for tour groups.

About 70 percent of the transportation services will be free.

However, two tourist bus lines will charge 10 yuan ($1.4), and the three water routes charge 60 yuan ($8.7), including a tour of the Huangpu River.

Transport authorities say they will control the flow of tourists to ensure safety.

"Large passenger volumes are our biggest concern and we will supervise the flow accurately when they enter the park; we can measure the volume using entry data from the World Expo Station," said Zhou.

"Tourists will be informed not to visit the park when the capacity reaches 400,000; they can visit other attractions in Shanghai instead and come on other days," Zhou explained.

Zhou added that entry to the expo will be blocked if capacity reaches 600,000.

Buses to the expo will stop taking tourists, and the subway will skip the World Expo Station.

"We hope tourists can understand we will do this to ensure safety and the smooth operation of the event," he said.