One man is believed to have been injured after a small device exploded in his rucksack at Warren Street station, near the West End's shops.
Shepherd's Bush and Oval Stations were also closed after similar incidents. The windows of a number 26 bus were blown out by a small blast in Hackney east London.
The Northern, Victoria and Hammersmith and City underground lines have been suspended. Westminster tube station has also been closed. There have been no reports of any fatalities.