diff --git a/sphinx/ext/autodoc/__init__.py b/sphinx/ext/autodoc/__init__.py
index 103537afa..3ce703b72 100644
--- a/sphinx/ext/autodoc/__init__.py
+++ b/sphinx/ext/autodoc/__init__.py
@@ -10,7 +10,6 @@
     :license: BSD, see LICENSE for details.
 """
 
-import importlib
 import re
 import warnings
 from inspect import Parameter, Signature
@@ -27,7 +26,7 @@ from sphinx.deprecation import (RemovedInSphinx40Warning, RemovedInSphinx50Warni
                                 RemovedInSphinx60Warning)
 from sphinx.environment import BuildEnvironment
 from sphinx.ext.autodoc.importer import (get_class_members, get_module_members,
-                                         get_object_members, import_object)
+                                         get_object_members, import_module, import_object)
 from sphinx.ext.autodoc.mock import mock
 from sphinx.locale import _, __
 from sphinx.pycode import ModuleAnalyzer, PycodeError
@@ -1809,12 +1808,14 @@ class UninitializedGlobalVariableMixin(DataDocumenterMixinBase):
         except ImportError as exc:
             # annotation only instance variable (PEP-526)
             try:
-                self.parent = importlib.import_module(self.modname)
-                annotations = get_type_hints(self.parent, None,
-                                             self.config.autodoc_type_aliases)
-                if self.objpath[-1] in annotations:
-                    self.object = UNINITIALIZED_ATTR
-                    return True
+                with mock(self.config.autodoc_mock_imports):
+                    parent = import_module(self.modname, self.config.autodoc_warningiserror)
+                    annotations = get_type_hints(parent, None,
+                                                 self.config.autodoc_type_aliases)
+                    if self.objpath[-1] in annotations:
+                        self.object = UNINITIALIZED_ATTR
+                        self.parent = parent
+                        return True
             except ImportError:
                 pass
 
@@ -2148,9 +2149,9 @@ class SlotsMixin(DataDocumenterMixinBase):
             return super().get_doc(encoding, ignore)  # type: ignore
 
 
-class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
+class RuntimeInstanceAttributeMixin(DataDocumenterMixinBase):
     """
-    Mixin for AttributeDocumenter to provide the feature for supporting uninitialized
+    Mixin for AttributeDocumenter to provide the feature for supporting runtime
     instance attributes (that are defined in __init__() methods with doc-comments).
 
     Example:
@@ -2160,6 +2161,8 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
                 self.attr = None  #: This is a target of this mix-in.
     """
 
+    RUNTIME_INSTANCE_ATTRIBUTE = object()
+
     def get_attribute_comment(self, parent: Any) -> Optional[List[str]]:
         try:
             for cls in inspect.getmro(parent):
@@ -2180,7 +2183,7 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
 
         return None
 
-    def is_uninitialized_instance_attribute(self, parent: Any) -> bool:
+    def is_runtime_instance_attribute(self, parent: Any) -> bool:
         """Check the subject is an attribute defined in __init__()."""
         # An instance variable defined in __init__().
         if self.get_attribute_comment(parent):
@@ -2189,9 +2192,8 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
             return False
 
     def import_object(self, raiseerror: bool = False) -> bool:
-        """Check the exisitence of uninitizlied instance attribute when failed to import
-        the attribute.
-        """
+        """Check the exisitence of runtime instance attribute when failed to import the
+        attribute."""
         try:
             return super().import_object(raiseerror=True)  # type: ignore
         except ImportError as exc:
@@ -2201,8 +2203,8 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
                                         attrgetter=self.get_attr,  # type: ignore
                                         warningiserror=self.config.autodoc_warningiserror)
                     parent = ret[3]
-                    if self.is_uninitialized_instance_attribute(parent):
-                        self.object = UNINITIALIZED_ATTR
+                    if self.is_runtime_instance_attribute(parent):
+                        self.object = self.RUNTIME_INSTANCE_ATTRIBUTE
                         self.parent = parent
                         return True
             except ImportError:
@@ -2216,11 +2218,11 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
                 return False
 
     def should_suppress_value_header(self) -> bool:
-        return (self.object is UNINITIALIZED_ATTR or
+        return (self.object is self.RUNTIME_INSTANCE_ATTRIBUTE or
                 super().should_suppress_value_header())
 
     def get_doc(self, encoding: str = None, ignore: int = None) -> List[List[str]]:
-        if self.object is UNINITIALIZED_ATTR:
+        if self.object is self.RUNTIME_INSTANCE_ATTRIBUTE:
             comment = self.get_attribute_comment(self.parent)
             if comment:
                 return [comment]
@@ -2229,14 +2231,14 @@ class UninitializedInstanceAttributeMixin(DataDocumenterMixinBase):
 
     def add_content(self, more_content: Optional[StringList], no_docstring: bool = False
                     ) -> None:
-        if self.object is UNINITIALIZED_ATTR:
+        if self.object is self.RUNTIME_INSTANCE_ATTRIBUTE:
             self.analyzer = None
 
         super().add_content(more_content, no_docstring=no_docstring)  # type: ignore
 
 
 class AttributeDocumenter(GenericAliasMixin, NewTypeMixin, SlotsMixin,  # type: ignore
-                          TypeVarMixin, UninitializedInstanceAttributeMixin,
+                          TypeVarMixin, RuntimeInstanceAttributeMixin,
                           NonDataDescriptorMixin, DocstringStripSignatureMixin,
                           ClassLevelDocumenter):
     """