BUG: pd.concat dataframes with different datetime64 resolutions

pandas/core/dtypes/concat.py

@@ -115,7 +115,16 @@ def concat_compat(
         # i.e. isinstance(to_concat[0], ExtensionArray)
         to_concat_eas = cast("Sequence[ExtensionArray]", to_concat)
         cls = type(to_concat[0])
-        return cls._concat_same_type(to_concat_eas)
+        # GH#53640: eg. for datetime array, axis=1 but 0 is default
+        # However, class method `_concat_same_type()` for some classes
+        # may not support the `axis` keyword
+        if ea_compat_axis or axis == 0:
+            return cls._concat_same_type(to_concat_eas)
+        else:
+            return cls._concat_same_type(
+                to_concat_eas,
+                axis=axis,  # type: ignore[call-arg]
+            )
     else:
         to_concat_arrs = cast("Sequence[np.ndarray]", to_concat)
         result = np.concatenate(to_concat_arrs, axis=axis)

pandas/tests/reshape/concat/test_concat.py

@@ -826,3 +826,17 @@ def test_concat_mismatched_keys_length():
         concat((x for x in sers), keys=(y for y in keys), axis=1)
     with tm.assert_produces_warning(FutureWarning, match=msg):
         concat((x for x in sers), keys=(y for y in keys), axis=0)
+
+
+def test_concat_datetime64_diff_resolution():
+    # GH#53640
+    df1 = DataFrame({"a": [0, 1], "b": [4, 5]}, dtype="datetime64[s]")
+    df2 = DataFrame({"a": [2, 3], "b": [6, 7]}, dtype="datetime64[ms]")
+    result = concat([df1, df2])
+
+    expected = DataFrame(
+        data={"a": [0, 1000, 2, 3], "b": [4000, 5000, 6, 7]},
+        index=[0, 1, 0, 1],
+        dtype="datetime64[ms]",
+    )
+    tm.assert_frame_equal(result, expected)