School supervisor Frank Fu Hoo-kin told the South China Morning Post Mrs Chan had chosen to leave for 'personal reasons', but declined to give details.

But parents have complained about a communication breakdown with the school and said they believed they were being kept in the dark over the real reasons for Mrs Chan's sudden departure.

'It seems very strange. I don't think we are being told the whole story,' said Chow Po-ngai, accompanying his son to school. 'There has to be something going on behind the scenes. 'Personal reasons' could mean anything. We don't think it is that simple.'

Mrs Chan's resignation was announced in a press release from the university late last Tuesday evening, effective September 1.

A letter was also posted on the school website. However, the notice has since been removed from the website, and the press release is not included in the university's online press archive.

Speaking to the Post this week, Mrs Chan would only say that the decision to leave had been her 'personal choice'.

'It was for various reasons, but of course some of them were personal,' she said. 'It is just a job. Sometimes it is time to move on.' She declined to comment on her relationship with the sponsoring body at this time. 'If I say something, I will make a full disclosure, but it will be at the appropriate time.'

Mrs Chan said she was 'a little sorry' that the lack of notice of her departure had sparked concern among parents. But she believed the school was in a strong position to carry on without her.

'I have put a lot of hard work into developing the school and putting the curriculum in place,' she said.

Professor Fu, who is also associate vice-president of BaptistU, denied there had been any breakdown in the relationship with Mrs Chan ahead of her resignation.

'We always worked well together. There were no problems,' he said. 'There is no crisis. Anyone is dispensable.'

He said the 'best type of leader is an invisible leader' and the change of principal would not affect the school's development.

He said he did not know the precise reasons for Mrs Chan's departure, but the timing was due to her wish for the school to be able to have a 'fresh start' in the new term. He added: 'She has not been fired. If the person does not want to give a reason for their resignation, we do not force them,' he said. 'We have to respect their decision.'

Professor Fu said he was due to meet parents this morning to discuss the school's future development.

'The meeting is not about Mrs Chan's resignation,' he said. 'But I will be happy to answer any questions parents may have.'

From the mood of parents outside the school this week, turnout is likely to be high.

'I think a lot of people will be asking a lot of questions,' said one mother, who would only give her name as Mrs Tang. 'We want some answers.' Mrs Tang said she felt uncertain about the school's future as Mrs Chan's reputation had been a key factor in choosing to send her daughter to the school.

'She came to our kindergarten several times over the past two years. She sold the vision for this school so well that she convinced us. I can't believe she would just leave like that.'

Chung Tin-sung, who was waiting to collect his grandson from class, voiced similar concerns. 'I am worried that our family has chosen the wrong school,' he said.