By Moazzem Hossain BBC reporter in Dhaka

The streets of the Bangladeshi capital, Dhaka, looked quite different on Monday, the first working day since a ban on polluting motorised rickshaws went into effect.

Who will give me a job? I only know how to drive an auto-rickshaw.

Auto-rickshaw driver Shah Alam

A ban on more than 12,000 auto-rickshaws went into effect from Sunday.

The familiar black and yellow coloured three wheelers - fitted with old two-stroke engines and fuelled by petrol, were held to be the main cause of Dhaka's alarmingly high level of air pollution.

They are being replaced with imported four-stroke-engine models from India and Thailand.

These new three-wheelers, painted green, are run on cleaner fuels like compressed natural gas (CNG).

But the drivers of the old models have gone on strike, and are in some cases trying to prevent the new vehicles plying their trade.

Environmental concerns

The government says that more than 18,000 of the old rickshaws have been phased out since January this year as part of an integrated plan to introduce a better and faster public transport system in Dhaka.

Drivers fear they will be unemployed

The move was welcomed by environmental groups and most residents of Dhaka, with only the auto-rickshaw drivers and owners affected protesting against it.

The drivers began a strike in Dhaka on Sunday to try to force their new green competitors off the street.

The striking drivers said the government did not give them enough time to make the changeover, which would mean buying a new greener vehicle.

Shah Alam, an auto-rickshaw driver, has become unemployed since the ban came into effect.

"I don't know what I will do now. Either I have to go back to my village, or look for an alternative job."

Enough time

The government said it had deferred the ban several times, allowing the auto-rickshaw drivers enough time to move their vehicles out of the city.

State Minister for Communication Salahuddin Ahmed said: "We also spared 5,500 auto-rickshaws from the ban for another four months. "

Although the absence of polluting three wheelers was a relief for people in Dhaka, commuters suffered as there was a lack of transport on the streets.

The government has given assurances that soon more public buses would be put on the streets by the state-run road transport corporation.