At present, 40% of revenue is lost through the sale of unauthorised tickets.

Huong said there is a need to fully explain to the public and tourists that the need for entrance tickets is tied to restoration work.

"About 90% of tourists do not know that entrance tickets to the old town and destinations are compulsory, or why," she said.

Vice chairman of the municipal People's Committee Truong Van Bay said the plan is to develop a multi-option tourist card from 2015.

Hoi An Party secretary Nguyen Su said 85% of ticket sales in Hoi An is used to restore old houses and relics of the UNESCO-recognised world heritage sites.

He also criticised some travel agencies for taking tourists to the town after 6pm, because entrance was then free.

"Some guides intentionally take tourists down alley ways to avoid paying," he said.

Foreigners pay VND120,000 (about US$6) and locals pay VND80,000 to visit the old town, which includes entrance to five major destinations.

However, the chairman of the city Le Van Giang said flexible ticket collections do not always work for tourists who want to wander around the old town on their own. He warned that some travel agencies still included entrance tickets in package tour prices, adding that poor attitudes by ticket inspectors upset some tourists