An investigation has begun in the Indian city of Calcutta after 18 babies died in the past three days at a state-run hospital.

Casualties on Tuesday were a three-year-old girl, who died of respiratory problems, and another child, the authorities say.

At least five to six children among hundreds brought into that hospital die daily

Health Minister Surya Kant Mishra

Reports say a shortage of oxygen and hospital beds may have contributed to the high death toll.

Angry, grieving parents have surrounded the hospital, with many taking their children for treatment elsewhere. The authorities deny their accusations of negligence.

The government-run BC Roy Hospital has beds for nearly 600 children, many of them acutely-ill, and officials say the deaths reflect normal mortality rates.

My pleas fell on deaf ears

Grieving mother

The state's Health Minister, Surya Kant Mishra, told the BBC that the deaths were not due to negligence on the part of the authorities.

"At least five to six children among hundreds brought into that hospital die daily," he said.

The West Bengal state government has ruled out a judicial enquiry into the deaths.

More than 30 children have died at the hospital over the past week

A report from the state health officer is awaited.

Anger

One mother said that she had pleaded with the nurses since Sunday morning to urgently attend to her son because his condition was deteriorating.

A grieving relative with one of the babies

"But my pleas fell on deaf ears," she told the Associated Press news agency.

A police cordon was put in place around the building as tempers flared.

On Sunday, 10 children at the hospital died, and on Monday the death toll was six.

Most are said to have been suffering from respiratory problems.

Last year,11 children died in a hospital in the northern city of Lucknow, allegedly due to a lack of oxygen cylinders.

Overcrowding and understaffing is a problem faced by many state-run hospitals in India.

"There are so many patients that get admitted in a serious condition that it is hardly surprising if several of them die in a single day," a BC Roy spokesman told reporters.