Hospitals in Delhi continued to send desperate messages for emergency oxygen supplies through the night on Sunday, warning that patients are at risk.

The crisis started two weeks ago but shows no signs of abating.

At least 12 patients, including a doctor, died when a prominent hospital ran out of oxygen on Saturday. Outside hospitals, families of patients who can't find a bed are struggling to get hold of portable cylinders - sometimes standing in queues for up to 12 hours.

Several big hospitals in Delhi are relying on daily oxygen supplies but they are not getting enough to keep some as backup in case of emergency.

One doctor described the situation as frightening, explaining: "Once you've used up your main tank, there is nothing to fall back on."

The situation is worse still in small hospitals that don't have storage tanks and have to rely on big cylinders.