India's annual monsoon rains have swept across the country about two weeks ahead of schedule, causing deadly floods.

Officials in the states of Assam and Arunchal Pradesh say at least 23 people have died in a series of floods, landslides and building collapses caused by the front edge of the monsoon.

Authorities say the army is on standby in case soldiers are needed to rescue trapped villagers.

The monsoon hit New Delhi yesterday - the earliest arrival of the rains in the city since record keeping began 108 years ago.

Subhash Chander Bhan, the director of the India Meteorological Department, says the early rains are due to an unusual weather system pulling moisture off the Bay of Bengal and dumping it on India.

The monsoon usually begins sweeping across the subcontinent in early June, but rarely reaches New Delhi and the rest of northern India before the beginning of July.