Foreign exchange bureaus in Tanzania's northern city of Arusha have remained closed for a second day after soldiers conducted what they called a "special operation" for reasons they have not given.

The operation ended at midnight but the bureaus have remained closed.

On Monday, most of them were being guarded by two unarmed army officers and no customer was allowed in the normally busy shops.

Some military officers were seen inside doing "audit work", local media reported.

Customers, mostly tourists and tour firms, have been struggling to change their money.

They have, however, been directed to change their currency at the central bank.