diff --git a/example/marker-clustering-realworld.50000.html b/example/marker-clustering-realworld.50000.html
index c439cccfd..1a1ecdc67 100644
--- a/example/marker-clustering-realworld.50000.html
+++ b/example/marker-clustering-realworld.50000.html
@@ -18,6 +18,7 @@
 </head>
 <body>
 
+    <div id="progress"><div id="progress-bar"></div></div>
 	<div id="map"></div>
 	<span>Mouse over a cluster to see the bounds of its children and click a cluster to zoom to those bounds</span>
 	<script type="text/javascript">
@@ -28,12 +29,28 @@
 
 			var map = L.map('map', { center: latlng, zoom: 13, layers: [cloudmade] });
 
-			var markers = L.markerClusterGroup({ chunkedLoading: true });
+            var progress = document.getElementById('progress');
+            var progressBar = document.getElementById('progress-bar');
+
+            function updateProgressBar(processed, total, elapsed, layersArray) {
+                if (elapsed > 1000) {
+                    // if it takes more than a second to load, display the progress bar:
+                    progress.style.display = 'block';
+                    progressBar.style.width = Math.round(processed/total*100) + '%';
+                }
+
+                if (processed === total) {
+                    // all markers processed - hide the progress bar:
+                    progress.style.display = 'none';
+                }
+            }
+
+            var markers = L.markerClusterGroup({ chunkedLoading: true, chunkProgress: updateProgressBar });
 
 			var markerList = [];
 
 			//console.log('start creating markers: ' + window.performance.now());
-			
+
 			for (var i = 0; i < addressPoints.length; i++) {
 				var a = addressPoints[i];
 				var title = a[2];
diff --git a/example/screen.css b/example/screen.css
index ea33d34ca..c89cba86c 100644
--- a/example/screen.css
+++ b/example/screen.css
@@ -2,4 +2,27 @@
 	width: 800px; 
 	height: 600px; 
 	border: 1px solid #ccc;
-	}
\ No newline at end of file
+}
+
+#progress {
+    display: none;
+    position: absolute;
+    z-index: 1000;
+    left: 400px;
+    top: 300px;
+    width: 200px;
+    height: 20px;
+    margin-top: -20px;
+    margin-left: -100px;
+    background-color: #fff;
+    background-color: rgba(255, 255, 255, 0.7);
+    border-radius: 4px;
+    padding: 2px;
+}
+
+#progress-bar {
+    width: 0;
+    height: 100%;
+    background-color: #76A6FC;
+    border-radius: 4px;
+}
diff --git a/src/MarkerClusterGroup.js b/src/MarkerClusterGroup.js
index dfa0bd053..a647c4702 100644
--- a/src/MarkerClusterGroup.js
+++ b/src/MarkerClusterGroup.js
@@ -27,9 +27,11 @@ L.MarkerClusterGroup = L.FeatureGroup.extend({
 		//Increase to increase the distance away that spiderfied markers appear from the center
 		spiderfyDistanceMultiplier: 1,
 
-		//When bulk adding layers, runs chunks at a time. Means addLayers may not add all the layers in the call, others will be loaded during setTimeouts
+		// When bulk adding layers, adds markers in chunks. Means addLayers may not add all the layers in the call, others will be loaded during setTimeouts
 		chunkedLoading: false,
-		chunkSize: 500,
+        chunkInterval: 200, // process markers for a maximum of ~ n milliseconds (then trigger the chunkProgress callback)
+        chunkDelay: 50, // at the end of each interval, give n milliseconds back to system/browser
+		chunkProgress: null, // progress callback: function(processed, total, elapsed) (e.g. for a progress indicator)
 
 		//Options to pass to the L.Polygon constructor
 		polygonOptions: {}
@@ -159,15 +161,25 @@ L.MarkerClusterGroup = L.FeatureGroup.extend({
 	addLayers: function (layersArray) {
 		var fg = this._featureGroup,
 			npg = this._nonPointGroup,
-			chunkSize = this.options.chunkSize,
+			chunkInterval = this.options.chunkInterval,
+			chunkProgress = this.options.chunkProgress,
 			newMarkers, i, l, m;
 
 		if (this._map) {
-			var start = 0;
-			var end = this.options.chunkedLoading && chunkSize < layersArray.length ? chunkSize : layersArray.length;
+			var offset = 0,
+				started = (new Date()).getTime();
 			var process = L.bind(function () {
-				for (i = start; i < end; i++) {
-					m = layersArray[i];
+				var start = (new Date()).getTime();
+				for (; offset < layersArray.length; offset++) {
+					if (offset % 200 === 0) {
+						// every couple hundred markers, instrument the time elapsed since processing started:
+						var elapsed = (new Date()).getTime() - start;
+						if (elapsed > chunkInterval) {
+							break; // been working too hard, time to take a break :-)
+						}
+					}
+
+					m = layersArray[offset];
 
 					//Not point data, can't be clustered
 					if (!m.getLatLng) {
@@ -191,7 +203,12 @@ L.MarkerClusterGroup = L.FeatureGroup.extend({
 					}
 				}
 
-				if (end === layersArray.length) {
+				if (chunkProgress) {
+					// report progress and time elapsed:
+					chunkProgress(offset, layersArray.length, (new Date()).getTime() - started);
+				}
+
+				if (offset === layersArray.length) {
 					//Update the icons of all those visible clusters that were affected
 					this._featureGroup.eachLayer(function (c) {
 						if (c instanceof L.MarkerCluster && c._iconNeedsUpdate) {
@@ -201,9 +218,7 @@ L.MarkerClusterGroup = L.FeatureGroup.extend({
 
 					this._topClusterLevel._recursivelyAddChildrenToMap(null, this._zoom, this._currentShownBounds);
 				} else {
-					start = end;
-					end = Math.min(end + chunkSize, layersArray.length);
-					setTimeout(process, 0);
+					setTimeout(process, this.options.chunkDelay);
 				}
 			}, this);
 
