It's the first time a team outside of London has won six successive top-flight matches in the capital for 67 years and is the Blues thirteenth win in 14 matches in the city.
City were too hot to handle in the opening 45 minutes, scoring three times in the space of 23 minutes through David Silva, Raheem Sterling and Leroy Sane.
The champions took their foot off the gas a little after the break until Sane added a fourth with almost the last kick of the game.
City were looking to pick up where they left off before the international break and had to wait just 11 minutes to take the lead at the London Stadium.
Fernandinho brought the ball forward before finding Sterling on the right – the England winger weighed up his options before sending in a deflected low ball that skipper Silva gently guided home from close range.
It was the Spaniard's fourth goal in as many games and his eight of an already stellar campaign.
The Blues doubled the lead just eight minutes later.
Silva was again involved as he collected the ball outside the Hammers’ box before spotting Sane in space – the German winger then danced past Pablo Zabaleta before crossing into the path of Sterling who made no mistake from four yards out.
This team make scoring goals look so easy - particularly at the London Stadium!
The Blues were lucky not to see that advantage halved moments later as a defensive mix-up gifted Arnautovic a chance that the Austrian couldn’t profit from as a mixture of Kyle Walker and Ederson snuffed out.
The hosts enjoyed a good five minutes of pressing City back, but they needed to reduce the deficit before the champions struck again – but that opportunity vanished on 34 minutes when the game was effectively ended as a contest as the Blues added a third - and what a goal it was.
Fernandinho's clever chip found Sterling’s dart into the box on the right and the winger volleyed a cross to the feet of Sane in the six-yard box and the Germany star first controlled the ball, sent a defender and the keeper the wrong way before coolly rolling the ball home.
It was clinical finishing from a side that, at times, look light years ahead of their opponents.
It also meant City had bagged 16 goals in just 315 minutes of action at the London Stadium.
The Hammers came out determined to put up some sort of fight after the break, but City should still have added a fourth a couple of minutes in as Silva's cross found Sterling and the City winger should have made it four but was tackled by Fabianski and Sane's follow-up was saved by the busy Pole.
West Ham came close again to reducing the arrears when Antonio broke clear on the right, but his low shot struck the outside of the post and the last chance to get something out of the game was lost.
City were in cruise control, happy with a three-goal lead and the Hammers seemed happy to compete a half without conceding again - but Sane had the final say in added time, controlling sub Gabriel Jesus' cross before volleying home to seal another happy visit to the capital.
City’s ruthless wingers
Two assists and a goal in the space of 23 first-half minutes – Sterling was at his devastating best for the Blues at the London Stadium.
That took him to eight goals and eight assists in 12 Premier League games, begging the question – is there a better right winger in European football at the moment?
And with Sane looking masterful on the left, the Blues’ wingers can destroy any defence when both our wingers are in the mood.
Sane also claimed two goals and an assist, with his two goals for Germany during the break clearly boosting his confidence.
What it means…
City remain top of the Premier League and still unbeaten with 13 games played, two clear of Liverpool who beat Watford 3-0.
Chelsea, the only previously unbeaten side.going into yesterday's fixtures, lost heavily to Spurs at Wembley.
Star man: Leroy Sane
Excellent stuff from the Germany winger.who just edged out fellow wide-man Sterling.
On his staff…
"I have an incredible staff and they know exactly when we have to train and when we have days off.
"They are the master at that, especially Lorenzo Buenaventura.
"How you handle regeneration is key.
"We push the players, it’s the only way."
On his squad…
"Nico Otamendi was incredible last season. Txiki and the people at City provide me with a great squad.
"If you want to compete, the players have to play good every time. If they don’t, next time they are not going to play."
On what pleases him most…
"The most important thing is that after what we achieved last season, we are still consistent and humble.
"Our passing today wasn't great but in terms of how we run without the ball it was fantastic.
"This season will be tough. Chelsea are so good - Tottenham didn’t spend one pound and they are they are there. Premier League remains tough, we can’t deny it."
City will look to secure a Champions League Round of 16 spot against Lyon next Tuesday.
The Blues need just a point to secure qualification with two games to play but will need to overcome a Lyon side that are the only team to win at the Etihad this season.
Then it’s back to Premier League action against Bournemouth next Saturday at the Etihad, 3pm kick-off.