diff --git a/packages/nuxt3/src/app/composables/asyncData.ts b/packages/nuxt3/src/app/composables/asyncData.ts
index d25d877b6a..db6f5455de 100644
--- a/packages/nuxt3/src/app/composables/asyncData.ts
+++ b/packages/nuxt3/src/app/composables/asyncData.ts
@@ -1,6 +1,7 @@
 import { Ref, ref, onMounted, watch, getCurrentInstance, onUnmounted } from 'vue'
 import { Nuxt, useNuxt } from 'nuxt/app'
-import { useData } from './data'
+
+import { ensureReactive, useData } from './data'
 
 export type AsyncDataFn<T> = (ctx?: Nuxt) => Promise<T>
 
@@ -12,7 +13,7 @@ export interface AsyncDataOptions {
 export interface AsyncDataObj<T> {
   data: Ref<T>
   pending: Ref<boolean>
-  refresh: Function
+  refresh: () => Promise<void>
   error?: any
 }
 
@@ -20,10 +21,10 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
   const nuxt = useNuxt()
   const vm = getCurrentInstance()
 
-  let data = useData(nuxt, vm)
+  const data = useData(nuxt, vm)
   let dataRef = 1
 
-  const onMountedCbs = []
+  const onMountedCbs: Array<() => void> = []
 
   if (process.client) {
     onMounted(() => {
@@ -31,13 +32,13 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
       onMountedCbs.splice(0, onMountedCbs.length)
     })
 
-    onUnmounted(() => {
-      onMountedCbs.splice(0, onMountedCbs.length)
-      data = null
-    })
+    onUnmounted(() => onMountedCbs.splice(0, onMountedCbs.length))
   }
 
-  return async function asyncData<T = any> (handler: AsyncDataFn<T>, options?: AsyncDataOptions): Promise<AsyncDataObj<T>> {
+  return async function asyncData<T = Record<string, any>> (
+    handler: AsyncDataFn<T>,
+    options?: AsyncDataOptions
+  ): Promise<AsyncDataObj<T>> {
     if (typeof handler !== 'function') {
       throw new TypeError('asyncData handler must be a function')
     }
@@ -51,6 +52,8 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
     const key = String(dataRef++)
     const pending = ref(true)
 
+    const datastore = ensureReactive(data, key)
+
     const fetch = async () => {
       pending.value = true
       const _handler = handler(nuxt)
@@ -59,11 +62,11 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
         // Let user resolve if request is promise
         // TODO: handle error
         const result = await _handler
-        if (!data[key]) {
-          data[key] = result
-        } else {
-          Object.assign(data[key], result)
+
+        for (const _key in result) {
+          datastore[_key] = result[_key]
         }
+
         pending.value = false
       } else {
         // Invalid request
@@ -81,14 +84,10 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
       }
       // 2. Initial load (server: false): fetch on mounted
       if (nuxt.isHydrating && !options.server) {
-        // Force tracking it
-        data[key] = {}
         // Fetch on mounted (initial load or deferred fetch)
         onMountedCbs.push(fetch)
       } else if (!nuxt.isHydrating) {
         if (options.defer) {
-          // Force tracking it
-          data[key] = {}
           // 3. Navigation (defer: true): fetch on mounted
           onMountedCbs.push(fetch)
         } else {
@@ -105,13 +104,16 @@ export function useAsyncData (defaults?: AsyncDataOptions) {
       await fetch()
     }
     return {
-      data: data[key],
+      data: datastore,
       pending,
       refresh: fetch
     }
   }
 }
 
-export function asyncData<T = any> (handler: AsyncDataFn<T>, options?: AsyncDataOptions): Promise<AsyncDataObj<T>> {
+export function asyncData<T = Record<string, any>> (
+  handler: AsyncDataFn<T>,
+  options?: AsyncDataOptions
+): Promise<AsyncDataObj<T>> {
   return useAsyncData()(handler, options)
 }
diff --git a/packages/nuxt3/src/app/composables/data.ts b/packages/nuxt3/src/app/composables/data.ts
index 5144edad73..0693eb83f5 100644
--- a/packages/nuxt3/src/app/composables/data.ts
+++ b/packages/nuxt3/src/app/composables/data.ts
@@ -1,12 +1,28 @@
-import { getCurrentInstance, reactive, isReactive } from 'vue'
+import { getCurrentInstance, isReactive, reactive, UnwrapRef } from 'vue'
+
 import { useNuxt } from 'nuxt/app'
 
+export function ensureReactive<
+  T extends Record<string, any>,
+  K extends keyof T
+> (data: T, key: K): UnwrapRef<T[K]> {
+  if (!isReactive(data[key])) {
+    data[key] = reactive(data[key] || ({} as T[K]))
+  }
+  return data[key]
+}
+
 /**
  * Returns a unique string suitable for syncing data between server and client.
  * @param nuxt (optional) A Nuxt instance
  * @param vm (optional) A Vue component - by default it will use the current instance
  */
 export function useSSRRef (nuxt = useNuxt(), vm = getCurrentInstance()): string {
+  if (!vm) {
+    throw new Error('This must be called within a setup function.')
+  }
+
+  // Server
   if (process.server) {
     if (!vm.attrs['data-ssr-ref']) {
       nuxt._refCtr = nuxt._refCtr || 1
@@ -15,9 +31,9 @@ export function useSSRRef (nuxt = useNuxt(), vm = getCurrentInstance()): string
     return vm.attrs['data-ssr-ref'] as string
   }
 
-  if (process.client) {
-    return vm.vnode.el?.dataset?.ssrRef || String(Math.random()) /* TODO: unique value for multiple calls */
-  }
+  // Client
+  /* TODO: unique value for multiple calls */
+  return vm.vnode.el?.dataset?.ssrRef || String(Math.random())
 }
 
 /**
@@ -25,14 +41,13 @@ export function useSSRRef (nuxt = useNuxt(), vm = getCurrentInstance()): string
  * @param nuxt (optional) A Nuxt instance
  * @param vm (optional) A Vue component - by default it will use the current instance
  */
-export function useData (nuxt = useNuxt(), vm = getCurrentInstance()): ReturnType<typeof reactive> {
+export function useData<T = Record<string, any>> (
+  nuxt = useNuxt(),
+  vm = getCurrentInstance()
+): UnwrapRef<T> {
   const ssrRef = useSSRRef(nuxt, vm)
 
   nuxt.payload.data = nuxt.payload.data || {}
 
-  if (!isReactive(nuxt.payload.data[ssrRef])) {
-    nuxt.payload.data[ssrRef] = reactive(nuxt.payload.data[ssrRef] || {})
-  }
-
-  return nuxt.payload.data[ssrRef]
+  return ensureReactive(nuxt.payload.data, ssrRef)
 }
diff --git a/packages/nuxt3/src/app/nuxt/composables.ts b/packages/nuxt3/src/app/nuxt/composables.ts
index 9cdca9ae4b..e61d1f2de0 100644
--- a/packages/nuxt3/src/app/nuxt/composables.ts
+++ b/packages/nuxt3/src/app/nuxt/composables.ts
@@ -1,9 +1,9 @@
 import { getCurrentInstance } from 'vue'
 import type { Nuxt } from 'nuxt/app'
 
-let currentNuxtInstance: Nuxt
+let currentNuxtInstance: Nuxt | null
 
-export const setNuxtInstance = (nuxt: Nuxt) => {
+export const setNuxtInstance = (nuxt: Nuxt | null) => {
   currentNuxtInstance = nuxt
 }
 
@@ -15,21 +15,20 @@ export const setNuxtInstance = (nuxt: Nuxt) => {
 export async function callWithNuxt (nuxt: Nuxt, setup: () => any) {
   setNuxtInstance(nuxt)
   const p = setup()
-  setNuxtInstance(undefined)
+  setNuxtInstance(null)
   await p
 }
 
 /**
  * Returns the current Nuxt instance.
  */
-export function useNuxt () {
+export function useNuxt (): Nuxt {
   const vm = getCurrentInstance()
 
-  if (!vm && !currentNuxtInstance) {
-    throw new Error('nuxt instance unavailable')
-  }
-
   if (!vm) {
+    if (!currentNuxtInstance) {
+      throw new Error('nuxt instance unavailable')
+    }
     return currentNuxtInstance
   }
 
diff --git a/packages/nuxt3/src/app/nuxt/index.ts b/packages/nuxt3/src/app/nuxt/index.ts
index 95ec40ed0c..f6ce4a9ea5 100644
--- a/packages/nuxt3/src/app/nuxt/index.ts
+++ b/packages/nuxt3/src/app/nuxt/index.ts
@@ -15,8 +15,8 @@ export interface Nuxt {
 
   ssrContext?: Record<string, any>
   payload: {
-    serverRendered?: true,
-    data?: object
+    serverRendered?: true
+    data?: Record<string, any>
     rendered?: Function
     [key: string]: any
   }
@@ -36,7 +36,6 @@ export interface CreateOptions {
 
 export function createNuxt (options: CreateOptions) {
   const nuxt: Nuxt = {
-    app: undefined,
     provide: undefined,
     globalName: 'nuxt',
     state: {},
@@ -69,6 +68,8 @@ export function createNuxt (options: CreateOptions) {
       serverRendered: true // TODO: legacy
     }
 
+    nuxt.ssrContext = nuxt.ssrContext || {}
+
     // Expose to server renderer to create window.__NUXT__
     nuxt.ssrContext.payload = nuxt.payload
   }