There has been a surge in the number of Sydney residents signing up for the Opal public transport smartcard, after take-up of the card ran behind expectations for months.

NSW Transport Minister Gladys Berejiklian said more than 250,000 Opal cards had been registered, and also announced the card's extension to several new bus routes, mostly in the eastern suburbs.

The Opal can now be used on the 326, 327, 355, 361 and L24 routes.

Ms Berejiklian's figure of Opal users represent a rapid growth in the number of people using the card, which has come in for criticism for the types of fares charged.