diff --git a/torchrl/envs/libs/jumanji.py b/torchrl/envs/libs/jumanji.py
index dbbc980e8cc..4ceaa35f56d 100644
--- a/torchrl/envs/libs/jumanji.py
+++ b/torchrl/envs/libs/jumanji.py
@@ -343,7 +343,9 @@ def __init__(
         self.categorical_action_encoding = categorical_action_encoding
         if env is not None:
             kwargs["env"] = env
+        batch_locked = kwargs.pop("batch_locked", kwargs.get("batch_size") is not None)
         super().__init__(**kwargs)
+        self._batch_locked = batch_locked
 
     def _build_env(
         self,
@@ -486,17 +488,17 @@ def _set_seed(self, seed):
             raise Exception("Jumanji requires an integer seed.")
         self.key = jax.random.PRNGKey(seed)
 
-    def read_state(self, state):
-        state_dict = _object_to_tensordict(state, self.device, self.batch_size)
+    def read_state(self, state, batch_size=None):
+        state_dict = _object_to_tensordict(state, self.device, self.batch_size if batch_size is None else batch_size)
         return self.state_spec["state"].encode(state_dict)
 
-    def read_obs(self, obs):
+    def read_obs(self, obs, batch_size=None):
         from jax import numpy as jnp
 
         if isinstance(obs, (list, jnp.ndarray, np.ndarray)):
             obs_dict = _ndarray_to_tensor(obs).to(self.device)
         else:
-            obs_dict = _object_to_tensordict(obs, self.device, self.batch_size)
+            obs_dict = _object_to_tensordict(obs, self.device, self.batch_size if batch_size is None else batch_size)
         return super().read_obs(obs_dict)
 
     def render(
@@ -579,25 +581,35 @@ def render(
 
     def _step(self, tensordict: TensorDictBase) -> TensorDictBase:
         import jax
+        if self.batch_locked:
+            batch_size = self.batch_size
+        else:
+            batch_size = tensordict.batch_size
 
         # prepare inputs
+        _state_example = self._state_example
+        if not self.batch_locked and _state_example.batch_size != tensordict.batch_size:
+            _state_example = _state_example.expand(tensordict.batch_size)
+        else:
+            _state_example = self._state_example
+
         state = _tensordict_to_object(tensordict.get("state"), self._state_example)
         action = self.read_action(tensordict.get("action"))
 
         # flatten batch size into vector
-        state = _tree_flatten(state, self.batch_size)
-        action = _tree_flatten(action, self.batch_size)
+        state = _tree_flatten(state, batch_size)
+        action = _tree_flatten(action, batch_size)
 
         # jax vectorizing map on env.step
         state, timestep = jax.vmap(self._env.step)(state, action)
 
         # reshape batch size from vector
-        state = _tree_reshape(state, self.batch_size)
-        timestep = _tree_reshape(timestep, self.batch_size)
+        state = _tree_reshape(state, batch_size)
+        timestep = _tree_reshape(timestep, batch_size)
 
         # collect outputs
-        state_dict = self.read_state(state)
-        obs_dict = self.read_obs(timestep.observation)
+        state_dict = self.read_state(state, batch_size=batch_size)
+        obs_dict = self.read_obs(timestep.observation, batch_size=batch_size)
         reward = self.read_reward(np.asarray(timestep.reward))
         done = timestep.step_type == self.lib.types.StepType.LAST
         done = _ndarray_to_tensor(done).view(torch.bool).to(self.device)
@@ -622,25 +634,35 @@ def _reset(
         import jax
         from jax import numpy as jnp
 
+        if self.batch_locked:
+            numel = self.numel()
+            batch_size = self.batch_size
+        else:
+            numel = tensordict.numel()
+            batch_size = tensordict.batch_size
+
         # generate random keys
-        self.key, *keys = jax.random.split(self.key, self.numel() + 1)
+        self.key, *keys = jax.random.split(self.key, numel + 1)
 
         # jax vectorizing map on env.reset
         state, timestep = jax.vmap(self._env.reset)(jnp.stack(keys))
 
         # reshape batch size from vector
-        state = _tree_reshape(state, self.batch_size)
-        timestep = _tree_reshape(timestep, self.batch_size)
+        state = _tree_reshape(state, batch_size)
+        timestep = _tree_reshape(timestep, batch_size)
 
         # collect outputs
-        state_dict = self.read_state(state)
-        obs_dict = self.read_obs(timestep.observation)
-        done_td = self.full_done_spec.zero()
+        state_dict = self.read_state(state, batch_size=batch_size)
+        obs_dict = self.read_obs(timestep.observation, batch_size=batch_size)
+        if not self.batch_locked:
+            done_td = self.full_done_spec.zero(batch_size)
+        else:
+            done_td = self.full_done_spec.zero()
 
         # build results
         tensordict_out = TensorDict(
             source=obs_dict,
-            batch_size=self.batch_size,
+            batch_size=batch_size,
             device=self.device,
         )
         tensordict_out.update(done_td)