Ferocious fighting is taking place in a major Afghan city, amid fears it could be the first provincial capital to fall to the Taliban.

Lashkar Gah in southern Helmand province is under heavy assault from the militants, despite persistent US and Afghan air strikes.

The Taliban are said to have seized a TV station. Thousands of people fleeing rural areas took shelter in buildings.

"There is fighting all around," a doctor told the BBC from his hospital.

Hundreds of Afghan reinforcements have been deployed to battle the militants. The Taliban have made rapid advances in recent months as US forces have withdrawn after 20 years of military operations in the country.

Helmand was the centrepiece of the US and British military campaign, and Taliban gains there would be a blow for the Afghan government.