A massive part of a glacier the size of 12 football fields in the Swiss Alps could break off, local authorities warned, after the discovery of an enormous crevasse in the glacier.

Swiss authorities have formed a crisis team to monitor the situation and blocked all hiking trails close to the Giesen glacier located at an altitude of 2,800 metres, below the north face of the Jungfrau peak in the Bernese alps.

Christian Abbuehl, who is heading the crisis team at the Lauterbrunnen commune, confirmed that the size of ice that risks breaking off to be about 12 football fields.

"But we do not know how thick the ice is, so we do not know the volume of water that could be generated if it melts," he said.

The large crack was discovered about a month ago, and prompted the Lauterbrunnen commune to issue a warning.

"A crevasse has been discovered at the Giesen glacier, which is found on the northeast side under the Jungfrau, leading to small pieces of ice falling off," said the commune.

"We cannot rule out that a large amount of ice could break off in the direction of Trimmleten-Sandbach," it added.

Abbuehl said the situation remains unchanged from the September warning, but noted that it could improve as the temperature falls.

While it has been unseasonably warm in early October, the weather is expected to turn by Friday, with snowfall expected in the Alps.

"At the moment, the danger is not so great as it is going to get colder. For the population there is also no immediate danger," noted Abbuehl.

"But we are observing the situation on a daily basis and we have closed off the hiking paths around the site," he added.

It is not uncommon for parts of glaciers to break off. At the same time, a cold front could also cause glaciers to form from melting snow.