Wild weather caused chaos at Melbourne Airport, delaying flights and forcing a runway to close on Thursday.

It was looking like the delays were going to inconvenience travellers again through Friday, but the airport's runways were reopened about 8am.

It's running smoothly for now, but if the weather worsens, the runways could be shut down again.

On Thursday, passengers were delayed because one runway was closed and an Airservices Australia spokeswoman said it was due to rain and low cloud in Melbourne.

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There was only runway that could operate the entire day.

The spokeswoman said people should check with airlines for details of delays on Friday.

Fairfax Media reported Qantas could only run 18 domestic flights an hour, they usually operate about 25.

It's been a wet week in Melbourne and Tuesday marked the wettest day of the year in the city.

Melbourne had more than 20mm of rain in a 24-hour period and broke the record for the wettest day by about 1mm.

Melbourne had not seen that much rain since the end of April.