Indonesia's vice-president said he thinks up to 25,000 may have died in the earthquake and flooding that ravaged the country's Sumatra island, state news agency Antara reported on Tuesday.

"We don't have confirmed data, but I think between 21,000 and 25,000 people have died," Vice-President Yusuf Kalla was quoted as saying in Medan city, where he stopped after making a trip to coordinate relief efforts in Sumatra.

The government has so far confirmed the deaths of around 5,000 people as a result of Sunday's quake and the tsunamis it triggered.

Most of the deaths have been in Aceh province, on the northern tip of Sumatra Island.

Large parts of the province, especially towns on its western coast that were facing the epicenter of the undersea quake, have yet to be visited by either reporters or rescue teams.