A strike by workers on the London Underground (Tube) caused severe disruption and delays for millions of travellers Tuesday, early reports showed.

Maintenance staff, drivers and station employees joined a 24-hour strike called by unions in protest against staff cuts which they claim pose a threat to security on the line and at unmanned stations.

More than three million people journey on the London Tube network, the oldest in the world, every day.

In the process of modernisation and cost-cutting, operators Transport for London (TfL) plan to axe 800 jobs, including on platforms and at ticket offices.

As services on most lines were suspended or delayed Tuesday, TfL called on passengers to seek other forms of transport. Many took to their bicycles, walked, or just stayed at home.

An extra 100 buses and 10,000 more passenger journeys on riverboat services on the Thames have been laid on. Escorted bike rides will also be operating.

Bob Crow, leader of the powerful RMT union, joined pickets at King's Cross station Tuesday. He apologised to travellers for the 'inconvenience' but said he was not shedding 'crocodile tears' over the walkout.

Spokesman Mike Brown of London Underground said: 'Londoners will face some disruption, but the city is not paralysed and people will still be able to get around.'