A network node (120) and method therein for performing multi-channel access procedures in a License-Assisted Access, LAA, cell in a wireless communication network are disclosed. The network node selects one carrier as a master carrier and starts a Listen Before Talk, LBT, channel sensing for all carriers at a same or different point in time. The network node further stores LBT channel sensing results for all carriers for at least the last two slot durations of a subframe and checks if the LBT channel sensing on the master carrier is successful based on its LBT channel sensing result. When the LBT channel sensing on the master carrier is successful, the network node checks the LBT channel sensing results for all other carriers, and transmits on the master carrier and the carriers where the LBT channel sensing is successful at the subframe boundary or earlier than the subframe boundary. When the subframe boundary of the master carrier is reached and the LBT channel sensing on the master carrier is not successful, the network node transmits on the carriers where the LBT channel sensing is successful at the subframe boundary or earlier than the subframe boundary.