It said increasing numbers of female foetuses were being aborted and baby girls deliberately neglected and left to die.

The report, entitled Disappearing Daughters, was compiled by UK charity ActionAid and Canada's International Development Research Centre (IDRC).

BBC quoted the report as saying that in one place in Punjab state, there were just 300 girls to every 1,000 boys among higher caste families,

ActionAid said India faced a 'bleak' future if it did not end its practice of cultural preference for boys.

Many Indian parents see girls as prohibitively expensive as they have to give large dowries when their daughters get married.

Girls also have fewer property rights.

More than 6,000 households across five states in north-western India were interviewed and statistical comparisons made with national census dates.

Under 'normal' circumstances, there should be about 950 girls for every 1,000 boys, the charity said.

But in three of the five sites surveyed, the number was below 800, it said.

In four sites, the proportion of girls to boys had declined since the 2001 census, the report said.

The research also found that ratios of girls to boys were declining fastest in comparatively prosperous urban areas.

ActionAid suggested that the increasing use of ultrasound technology may be a factor in the trend.

The report said that Indian women were put under intense pressure to produce sons.

It said many families now used ultrasound scans and aborted female foetuses, despite the existence of a 1994 law banning gender selection and selective abortion.

The charity also blamed other illegal practices - for instance, allowing the umbilical cord to become infected - for the growing gender imbalance.

'The real horror of the situation is that, for women, avoiding having daughters is a rational choice,' said Ms Laura Turquet, women's rights policy official at ActionAid.

'But for wider society it's creating an appalling and desperate state of affairs.'

She added: 'In the long term, cultural attitudes need to change. India must address economic and social barriers including property rights, marriage dowries and gender roles that condemn girls before they are even born.

'If we don't act now, the future looks bleak.'

Some 10 million female foetuses have been aborted in India in the past 20 years, British medical journal The Lancet has said.