A visit by 34 children from China to show off their talent for mathematics looks set to be banned under tight rules against illegal immigrants. The children from Guangzhou were due to arrive on Sunday to join about 150 Hong Kong and Thai children who can do sums in seconds without using calculators. They are all students of Simon Wu Sing methods, known for teaching children how to sharpen their minds through sums. Ada Chick of the Simon Wu Training Centre said: 'The schools in Guangzhou originally told us about 40 children and teachers would arrive in Hong Kong on Sunday. They said all the permits were ready. 'But now they say their permits are being held by the authorities because of the recent influx of illegal migrants.' Simon Wu was in Guangzhou last night negotiating with officers to allow the youngsters' visit to go ahead. Ms Chick added: 'We have spent more than $4,000 booking a camp in Tai Po for the children to stay between May 3 and 5, and another $2,000 on meals.' The demonstration is due to take place in the Music Hall of the Cultural Centre on Sunday, with teachers reading out a string of numbers. The children were first taught how to use an abacus before being taught how to do calculations using a mental picture of an abacus. The Guangdong Public Security Bureau announced last week that mainlanders would be restricted from travelling to Hong Kong from June 15 to July 15 to ensure the handover is not disrupted by an influx of visitors.