Bomb disposal experts and police are meeting at a site in Suffolk where workmen uncovered and then set off a buried explosive device.
Four streets had to be cordoned off
The men were digging a hole in Wilde's Street, Lowestoft, on Thursday evening, when it filled with flames. The workers then used earth to put out the fire.
The incident happened near gas storage tanks, which were emptied to reduce any risk and the area was cordoned off.
The bomb disposal team will examine the site on Friday and decide what do next.
Police are working on the theory the device was a World War II bomb.
Officers say no-one was hurt in the incident and an evacuation of the area was not needed.