Police were called to Welshpool Close in Bransholme, Hull, this morning following the discovery.
Officers initially put in a 100m safety cordon to make the public safe, but this has now been extended to a 400m cordon.
Humberside Police is now waiting for specially trained Explosive Ordnance Disposal officers to arrive at the scene to deal with the package.
A statement from the force said: Officers issued a 100 metre safety cordon on Welshpool Close, Bransholme, following the discovery of a suspicious package earlier today (Saturday, 14 May).
"The cordon has now been extended to 400 metres whilst awaiting EOD to arrive at the scene to examine the item.
"Evacuations are taking place and residents are being advised of the procedures to follow. Please avoid the area until we are able to advise otherwise."