Monday’s shutdown affected up to 16,000 passengers who were due to fly, although some airlines switched their flights to other London hubs.
The bomb was discovered at around 5:00am (0500 GMT) on Sunday and a 214-metre exclusion zone was imposed “to ensure that the ordnance can be safely dealt with whilst limiting any risk to the public,” police said.
Homes within the exclusion zone were evacuated overnight and the local authority was providing residents with temporary accommodation and support.
“Officers are assisting with a controlled evacuation of up to 500 people,” the Newham Council local authority said in a statement, adding that a former town hall building had been opened up for evacuees.
It said specialist officers “have attended and confirmed it as a German 500-kilogramme fused device”.
Newham Council said: “Work will not start on lifting and removing the device until the initial 214-metre zone is clear.