diff --git a/webapp/src/archiver.ts b/webapp/src/archiver.ts
index 1359e5935..9fc6f416d 100644
--- a/webapp/src/archiver.ts
+++ b/webapp/src/archiver.ts
@@ -2,6 +2,7 @@
 // See LICENSE.txt for license information.
 import {ArchiveUtils, IArchiveHeader, IArchiveLine, IBlockArchiveLine} from './blocks/archive'
 import {IBlock, IMutableBlock} from './blocks/block'
+import {LineReader} from './lineReader'
 import mutator from './mutator'
 import {Utils} from './utils'
 import {BoardTree} from './viewModel/boardTree'
@@ -37,46 +38,40 @@ class Archiver {
     }
 
     private static async readBlocksFromFile(file: File): Promise<IBlock[]> {
-        // TODO: Read input as a stream, line by line
-        const contents = await (new Response(file)).text()
-        Utils.log(`Import ${contents.length} bytes.`)
-
         const blocks: IBlock[] = []
-        const allLineStrings = contents.split('\n')
-        if (allLineStrings.length >= 2) {
-            const headerString = allLineStrings[0]
-            const header = JSON.parse(headerString) as IArchiveHeader
-            if (header.date && header.version >= 1) {
-                const date = new Date(header.date)
-                Utils.log(`Import archive, version: ${header.version}, date/time: ${date.toLocaleString()}, ${blocks.length} block(s).`)
 
-                const lineStrings = allLineStrings.slice(1)
-                for (const lineString of lineStrings) {
-                    if (!lineString) {
-                        // Ignore empty lines, e.g. last line
-                        continue
+        let isFirstLine = true
+        return new Promise<IBlock[]>((resolve) => {
+            LineReader.readFile(file, (line, completed) => {
+                if (completed) {
+                    resolve(blocks)
+                    return
+                }
+
+                if (isFirstLine) {
+                    isFirstLine = false
+                    const header = JSON.parse(line) as IArchiveHeader
+                    if (header.date && header.version >= 1) {
+                        const date = new Date(header.date)
+                        Utils.log(`Import archive, version: ${header.version}, date/time: ${date.toLocaleString()}.`)
                     }
-
-                    const line = JSON.parse(lineString) as IArchiveLine
-                    if (!line || !line.type || !line.data) {
+                } else {
+                    const row = JSON.parse(line) as IArchiveLine
+                    if (!row || !row.type || !row.data) {
                         Utils.logError('importFullArchive ERROR parsing line')
-                        continue
+                        return
                     }
-                    switch (line.type) {
+                    switch (row.type) {
                     case 'block': {
-                        const blockLine = line as IBlockArchiveLine
+                        const blockLine = row as IBlockArchiveLine
                         const block = blockLine.data
                         blocks.push(block)
                         break
                     }
                     }
                 }
-            } else {
-                Utils.logError('importFullArchive ERROR parsing header')
-            }
-        }
-
-        return blocks
+            })
+        })
     }
 
     static importFullArchive(onComplete?: () => void): void {
diff --git a/webapp/src/lineReader.ts b/webapp/src/lineReader.ts
new file mode 100644
index 000000000..c8b395ef3
--- /dev/null
+++ b/webapp/src/lineReader.ts
@@ -0,0 +1,75 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+class LineReader {
+    private static appendBuffer(buffer1: ArrayBuffer, buffer2: ArrayBuffer) {
+        const tmp = new Uint8Array(buffer1.byteLength + buffer2.byteLength)
+        tmp.set(new Uint8Array(buffer1), 0)
+        tmp.set(new Uint8Array(buffer2), buffer1.byteLength)
+        return tmp.buffer
+    }
+
+    private static arrayBufferIndexOf(buffer: ArrayBuffer, charCode: number): number {
+        const view = new Uint8Array(buffer)
+        for (let i = 0; i < view.byteLength; ++i) {
+            if (view[i] === charCode) {
+                return i
+            }
+        }
+
+        return -1
+    }
+
+    static readFile(file: File, callback: (line: string, completed: boolean) => void): void {
+        let buffer = new ArrayBuffer(0)
+
+        const chunkSize = 1024 * 1000
+        let offset = 0
+        const fr = new FileReader()
+        const decoder = new TextDecoder()
+
+        fr.onload = () => {
+            const chunk = fr.result as ArrayBuffer
+            buffer = LineReader.appendBuffer(buffer, chunk)
+
+            const newlineChar = 10 // '\n'
+            let newlineIndex = LineReader.arrayBufferIndexOf(buffer, newlineChar)
+            while (newlineIndex >= 0) {
+                const result = decoder.decode(buffer.slice(0, newlineIndex))
+                buffer = buffer.slice(newlineIndex + 1)
+                callback(result, false)
+                newlineIndex = LineReader.arrayBufferIndexOf(buffer, newlineChar)
+            }
+
+            offset += chunkSize
+            if (offset >= file.size) {
+                // Completed
+
+                if (buffer.byteLength > 0) {
+                    // Handle last line
+                    callback(decoder.decode(buffer), false)
+                }
+
+                callback('', true)
+                return
+            }
+
+            seek()
+        }
+
+        fr.onerror = () => {
+            callback('', true)
+        }
+
+        seek()
+
+        function seek() {
+            const slice = file.slice(offset, offset + chunkSize)
+
+            // Need to read as an ArrayBuffer (instead of text) to handle unicode boundaries
+            fr.readAsArrayBuffer(slice)
+        }
+    }
+}
+
+export {LineReader}