Rescuers have begun drilling an escape shaft to save 33 miners trapped after a cave-in at Chile's San Jose gold and copper mine.

The bid to rescue the miners, stuck in a hot and humid tunnel half a mile underground, could take between two and four months. The government has turned to Nasa and submarine experts for help.

Striving to keep the men physically and mentally fit for the wait ahead, doctors sent flu vaccinations and nicotine gum for smokers in withdrawal down a tiny shaft the size of a grapefruit, the men's umbilical cord to the outside world.

Rescuers started drilling a 2ft-diameter shaft on Monday evening that will be used to evacuate the miners one at a time in a cage attached to a pulley.

Engineers are also looking into other options to speed up the rescue, including digging a second escape duct that could take about 60 days.