They are searching for man seen running from the station. Sniffer dogs looking for a person above ground.
No indication who they are looking for.
Explosions were detonators..rather than bombs themselves.
One injury confirmed.
If they get the explosives intact that would be a big win for tracing to the source.
TUBE EXPLOSION REPORTED
There have been unconfirmed reports of an explosion on the London Underground, and an incident on a bus in Hackney, East London.
There have been no reports of casualties.
Stations at Warren Street, Oval and Shepherd's Bush have been closed.
Services on the Victoria, Northern and Hammersmith & City Lines have been suspended.
Emergency servies started receiving calls just after 12.30.
At Warren Street there were reports of a nail bomb explosion. Sky's Crime Correspondent Martin Brunt said police believe this may have been the sound of detonators going off.
Victoria Line train passenger Ivan McCracken told Sky News he spoke to an Italian man who witnessed an explosion just after the train arrived at the platform.
"He told me he had seen a man carrying a rucksack which suddenly exploded. It was a minor explosion but enough to blow open his rucksack. Everyone rushed from the carriage. People evacuated very quickly. There was no panic.
"I didn't see anyone injured but there was shock and fright.
"There was a smell of smoke."
"The man who was holding the rucksack looked extremely dismayed.
Police have cordoned off the streets around Warren Street station. They said a suspect package had been reported on a Victoria Line train.
Sky reporter Mark White said authorities are "pushing everybody as far back from the station as they can".
"Police activity suggests that they are looking for somebody on the outside here."
Another eyewitness, Sosiane Mohellavi, said "Everyone panicked and people were screaming. We had to pull the alarm. I am still shaking."
Scotland Yard said emergency services have responded to an "incident" on a bus in Hackney Road, on a junction near Colombia Road, east London.
Sky News Foreign Affairs editor Tim Marshall said: "There is a bus parked there which is empty and there is nobody anywhere near it."
This does indicate that police think the bus is still dangerous.
It is two weeks to the day since bombers attacked three Tube trains and a bus in central London.