The walkout by more than 3,000 Unite members, in a row over pay, is set to enter its fourth day, despite pleas from West Midlands Mayor Andy Street to come to an agreement "for the good of the people".
On Thursday afternoon, a statement from National Express West Midlands said: "We have been advised that the bus strikes are set to continue. Sadly this means that you should plan alternative travel arrangements for the next few days and the weekend. We continue to run a limited service, primarily to the region's major hospitals."
The strikes are only affecting National Express services, with other operators running their full timetables.
What National Express buses are running?
The strikes continue to cripple the company's bus services in operation.
Bosses at National Express West Midlands have continued to prioritise routes serving hospitals in the region. In an update on Wednesday afternoon, the operator listed the following routes as running today and tomorrow morning:
4 Birmingham - Solihull (via Sparkbrook, Tyseley, Acocks Green & Olton)
5 West Bromwich - Sutton Coldfield (via Great Barr, Kingstanding & New Oscott)
6 Birmingham - Solihull (via Sparkbrook, Sparkhill, Hall Green & Shirley)
6 Dudley - Stourbridge (via Russells Hall Hospital, Brierley Hill & Amblecote)
28 Heartlands Hospital - Great Barr (via Ward End, Castle Bromwich, Erdington, Old Oscott & Perry Beeches)
51 Birmingham - Walsall (via Great Barr & Perry Barr)
59 Wolverhampton - Ashmore Park (via New Cross Hospial & Wednesfield)
87 Birmingham - Oldbury (via City Hospital & Smethwick)
97 Birmingham - Chelmsley Wood (via Bordesley Green, Heartlands Hospital & Meadway)
529 Wolverhampton - Walsall (via Willenhall)
X4 Birmingham - Falcon Lodge (via Aston Expressway, Erdington, Sutton Coldfield & Good Hope Hospital)
X21Birmingham - Weoley Castle (via Birmingham University & Selly Oak
Company bosses add: "We will try to operate more depending on driver availability."
How long is the bus strike for?
The strike will continue going until the National Express and union chiefs agree on a deal.
Until then, National Express bus drivers will remain on the picket line with the most recent offer, of a 14.3 per cent rise, being rejected.