A water main break in London, Ont., has caused a huge sinkhole in the city's core.

Several large buildings have been closed and at least one high school has sent students home when power had to be shut down.

Water flooded the intersection of Dundas and Wellington streets just before five a.m.A short time later the sinkhole, which is about 10 metres in diameter, opened up.

City engineer Peter Steblin said the damage is extensive.

"In congested downtown cores, just like it's congested on the surface, it is very congested underground with many different utilities in close proximity.And so when there is a water main break, there's a lot of water," Steblin said.

"It comes out at high pressure and there's a lot of damage that does occur. In this particular case there are hydro vaults and lines in very close proximity that have been impacted."

The city has activated its emergency operations centre and will set up public information lines as soon as possible.

City Hall was also affected by the flooding and a power outage.

It isn't known how that part of the flood will affect the city's response.