Kabul - At least 20 people were killed Friday in back-to-back earthquakes in eastern Afghanistan.

The first quake, with a magnitude of 5.4, struck shortly after midnight in Nangarhar province, a statement from President Hamid Karzai said.

A few hours later, a magnitude-5.1 tremor struck in the same region in the Hindu Kush mountains, the statement said.

At least 50 people were injured by falling rubble, and authorities were searching for more victims, officials said.

The Afghanistan National Disaster Management Authority said the epicentre and the worst damage was in the Shersad district, about 80 kilometres east of Kabul.

Several villages saw the collapse of 200 to 300 houses, which are constructed primarily out of earth, said the authority's director, Abdul Mateen Edrak.

The quake zone near the border with Pakistan had also seen heavy rains in the past several days, so many of the collapsed buildings were already damaged when the quakes struck, the authority said.

The Hindu Kush sees frequent earthquakes. A magnitude-6.4 quake in January caused damage along the Afghan-Pakistan border and into Kashmir.

Kashmir and Pakistan's North-West Frontier Province were also hit by a magnitude-7.6 quake in 2005 that killed about 74,000 people in Pakistan and India. (dpa)