A suspected unexploded World War Two bomb discovered on the banks of the River Thames could threaten the university Boat Race.
The find was made near Putney Bridge, west London, a day before the 163rd Oxford v Cambridge race.
Police said it was too early to say what effect it would have on the race.
The device is submerged and a bomb disposal unit will have to wait until the tide goes out in order to take a better look at it, police said.
The Thames river tide will not recede until around 01:00 BST on Sunday.
The Met said the organisers of the boat race would have been informed of the situation, but that it was to early to say if the race would be called off.
Roads in the area currently remain open.
In a statement, the Met confirmed officers were in attendance on the northern bank of the Thames at Chelsea.
It said: "Police were called by a member of the public at approximately 13:50 BST on Saturday 1 April reporting what they thought to be World War Two ordnance on the Chelsea shoreline by Putney Bridge.
"Officers including the Marine Policing Unit are in attendance."